Self-ionized and inductively-coupled plasma for sputtering and resputtering

ABSTRACT

A magnetron sputter reactor for sputtering deposition materials such as tantalum, tantalum nitride and copper, for example, and its method of use, in which self-ionized plasma (SIP) sputtering and inductively coupled plasma (ICP) sputtering are promoted, either together or alternately, in the same or different chambers. Also, bottom coverage may be thinned or eliminated by ICP resputtering in one chamber and SIP in another. SIP is promoted by a small magnetron having poles of unequal magnetic strength and a high power applied to the target during sputtering. ICP is provided by one or more RF coils which inductively couple RF energy into a plasma. The combined SIP-ICP layers can act as a liner or barrier or seed or nucleation layer for hole. In addition, an RF coil may be sputtered to provide protective material during ICP resputtering. In another chamber an array of auxiliary magnets positioned along sidewalls of a magnetron sputter reactor on a side towards the wafer from the target. The magnetron preferably is a small, strong one having a stronger outer pole of a first magnetic polarity surrounding a weaker outer pole of a second magnetic polarity and rotates about the central axis of the chamber. The auxiliary magnets preferably have the first magnetic polarity to draw the unbalanced magnetic field component toward the wafer. The auxiliary magnets may be either permanent magnets or electromagnets.

RELATED APPLICATIONS

This application is a continuation of pending application Ser. No.10/495,506 filed May 12, 2004, which is a 371 of PCT/US02/36940 filedNov. 14, 2002, which is a continuation in part application ofapplication Ser. No. 09/685,978 filed Oct. 10, 2000 (issued as U.S. Pat.No. 6,582,569), which is a divisional application of application Ser.No. 09/414,614 filed Oct. 8, 1999 (issued as U.S. Pat. No. 6,398,929);and said PCT/US02/36940 is a continuation in part of application Ser.No. 10/202,778, filed Jul. 25, 2002 (now abandoned), which claimspriority to provisional applications 60/316,137 filed Aug. 30, 2001, and60/342,608 filed Dec. 21, 2001); and said PCT/US02/36940 is acontinuation in part application of application Ser. No. 09/993,543,filed Nov. 14, 2001 (issued as U.S. Pat. No. 6,610,184), all of whichare incorporated by reference in their entireties.

FIELD OF THE INVENTION

The invention relates generally to sputtering and resputtering. Inparticular, the invention relates to the sputter deposition of materialand resputtering of deposited material in the formation of semiconductorintegrated circuits.

BACKGROUND ART

Semiconductor integrated circuits typically include multiple levels ofmetallization to provide electrical connections between large numbers ofactive semiconductor devices. Advanced integrated circuits, particularlythose for microprocessors, may include five or more metallizationlevels. In the past, aluminum has been the favored metallization, butcopper has been developed as a metallization for advanced integratedcircuits.

A typical metallization level is illustrated in the cross-sectional viewof FIG. 1. A lower-level layer 110 includes a conductive feature 112. Ifthe lower-level layer 110 is a lower-level dielectric layer, such assilica or other insulating material, the conductive feature 112 may be alower-level copper metallization, and the vertical portion of theupper-level metallization is referred to as a via since it interconnectstwo levels of metallization. If the lower-level layer 110 is a siliconlayer, the conductive feature 112 may a doped silicon region, and thevertical portion of the upper-level metallization formed in a hole isreferred to as a contact because it electrically contacts silicon. Anupper-level dielectric layer 114 is deposited over the lower-leveldielectric layer 110 and the lower-level metallization 112. There areyet other shapes for the holes including lines and trenches. Also, indual damascene and similar interconnect structures, as described below,the holes have a complex shape. In some applications, the hole may notextend through the dielectric layer. The following discussion will referto only via holes, but in most circumstances the discussion appliesequally well to other types of holes with only a few modifications wellknown in the art.

Conventionally, the dielectric is silicon oxide formed byplasma-enhanced chemical vapor deposition (PECVD) usingtetraethylorthosilicate (TEOS) as the precursor. However, low-kmaterials of other compositions and deposition techniques are beingconsidered. Some of the low-k dielectrics being developed can becharacterized as silicates, such as fluorinated silicate glasses.Hereafter, only silicate (oxide) dielectrics will be directly described,but it is contemplated that other dielectric compositions may be used.

A via hole is etched into the upper-level dielectric layer 114 typicallyusing, in the case of silicate dielectrics, a fluorine-based plasmaetching process. In advanced integrated circuits, the via holes may havewidths as low as 0.18 μm or even less. The thickness of the dielectriclayer 114 is usually at least 0.7 μm, and sometimes twice this, so thatthe aspect ratio of the hole may be 4:1 or greater. Aspect ratios of 6:1and greater are being proposed. Furthermore, in most circumstances, thevia hole should have a vertical profile.

A liner layer 116 may be deposited onto the bottom and sides of the holeand above the dielectric layer 114. The liner 116 can perform severalfunctions. It can act as an adhesion layer between the dielectric andthe metal since metal films tend to peel from oxides. It can also act asa barrier against inter-diffusion between the oxide-based dielectric andthe metal. It may also act as a seed and nucleation layer to promote theuniform adhesion and growth and possibly low-temperature reflow for thedeposition of metal filling the hole and to nucleate the even growth ofa separate seed layer. One or more liner layers may be deposited, inwhich one layer may function primarily as a barrier layer and others mayfunction primarily as adhesion, seed or nucleation layers.

An interconnect layer 118 of a conductive metal such as copper, forexample, is then deposited over the liner layer 116 to fill the hole andto cover the top of the dielectric layer 114. Conventional aluminummetallizations are patterned into horizontal interconnects by selectiveetching of the planar portion of the metal layer 118. However, atechnique for copper metallization, called dual damascene, forms thehole in the dielectric layer 114 into two connected portions, the firstbeing narrow vias through the bottom portion of the dielectric and thesecond being wider trenches in the surface portion which interconnectthe vias. After the metal deposition, chemical mechanical polishing(CMP) is performed which removes the relatively soft copper exposedabove the dielectric oxide but which stops on the harder oxide. As aresult, multiple copper-filled trenches of the upper level, similar tothe conductive feature 112 of the next lower level, are isolated fromeach other. The copper filled trenches act as horizontal interconnectsbetween the copper-filled vias. The combination of dual damascene andCMP eliminates the need to etch copper. Several layer structures andetching sequences have been developed for dual damascene, and othermetallization structures have similar fabrication requirements.

Lining and filling via holes and similar high aspect-ratio structures,such as occur in dual damascene, have presented a continuing challengeas their aspect ratios continue to increase. Aspect ratios of 4:1 arecommon and the value will further increase. An aspect ratio as usedherein is defined as the ratio of the depth of the hole to narrowestwidth of the hole, usually near its top surface. Via widths of 0.18 μmare also common and the value will further decrease. For advanced copperinterconnects formed in oxide dielectrics, the formation of the barrierlayer tends to be distinctly separate from the nucleation and seedlayer. The diffusion barrier may be formed from a bilayer of Ta/TaN,W/WN, or Ti/TiN, or of other structures. Barrier thicknesses of 10 to 50nm are typical. For copper interconnects, it has been found useful todeposit one or more copper layers to fulfill the nucleation and seedfunctions.

The deposition of the liner layer or the metallization by conventionalphysical vapor deposition (PVD), also called sputtering, is relativelyfast. A DC magnetron sputtering reactor has a target which is composedof the metal to be sputter deposited and which is powered by a DCelectrical source. The magnetron is scanned about the back of the targetand projects its magnetic field into the portion of the reactor adjacentthe target to increase the plasma density there to thereby increase thesputtering rate. However, conventional DC sputtering (which will bereferred to as PVD in contrast to other types of sputtering to beintroduced) predominantly sputters neutral atoms. The typical iondensities in PVD are often less than 10⁹ cm⁻³. PVD also tends to sputteratoms into a wide angular distribution, typically having a cosinedependence about the target normal. Such a wide distribution can bedisadvantageous for filling a deep and narrow via hole 122 such as thatillustrated in FIG. 2, in which a barrier layer 124 has already beendeposited. The large number of off-angle sputter particles can cause alayer 126 to preferentially deposit around the upper corners of the hole122 and form overhangs 128. Large overhangs can further restrict entryinto the hole 122 and cause inadequate coverage of the sidewalls 130 andbottom 132 of the hole 122. Also, the overhangs 128 can bridge the hole122 before it is filled and create a void 134 in the metallizationwithin the hole 122. Once a void 134 has formed, it is often difficultto reflow it out by heating the metallization to near its melting point.Even a small void can introduce reliability problems. If a secondmetallization deposition step is planned, such as by electroplating, thebridged overhang make subsequent deposition more difficult.

One approach to ameliorate the overhang problem is long-throw sputteringin which the sputtering target is spaced relatively far from the waferor other substrate being sputter coated. For example, thetarget-to-wafer spacing can be at least 50% of wafer diameter,preferably more than 90%, and more preferably more than 140%. As aresult, the off-angle portion of the sputtering distribution ispreferentially directed to the chamber walls, but the central-angleportion remains directed substantially to the wafer. The truncatedangular distribution can cause a higher fraction of the sputterparticles to be directed deeply into the hole 122 and reduce the extentof the overhangs 128. A similar effect can be accomplished bypositioning a collimator between the target and wafer. Because thecollimator has a large number of holes of high aspect ratio, theoff-angle sputter particles tend to strike the sidewalls of thecollimator, and the central-angle particles tend to pass through. Bothlong-throw targets and collimators typically reduce the flux of sputterparticles reaching the wafer and thus tend to reduce the sputterdeposition rate. The reduction can become more pronounced as throws arelengthened or as collimation is tightened to accommodate via holes ofincreasing aspect ratios.

Also, the length that long throw sputtering may be increased may belimited. At the few milliTorr of argon pressure often used in PVDsputtering, there is a greater possibility of the argon scattering thesputtered particles as the target to wafer spacing increases. Hence, thegeometric selection of the forward particles may be decreased. A yetfurther problem with both long throw and collimation is that the reducedmetal flux can result in a longer deposition period which can not onlyreduce throughput, but also tends to increase the maximum temperaturethe wafer experiences during sputtering. Still further, long throwsputtering can reduce over hangs and provide good coverage in the middleand upper portions of the sidewalls, but the lower sidewall and bottomcoverage can be less than satisfactory.

Another technique for deep hole lining and filling is sputtering using ahigh-density plasma (HDP) in a sputtering process called ionized metalplating (IMP). A typical high-density plasma is one having an averageplasma density across the plasma, exclusive of the plasma sheaths, of atleast 10¹¹ cm⁻³, and preferably at least 10¹² cm⁻³. In IMP deposition, aseparate plasma source region is formed in a region away from the wafer,for example, by inductively coupling RF power into a plasma from anelectrical coil wrapped around a plasma source region between the targetand the wafer. The plasma generated in this fashion is referred to as aninductively coupled plasma (ICP). An HDP chamber having thisconfiguration is commercially available from Applied Materials of SantaClara, Calif. as the HDP PVD Reactor. Other HDP sputter reactors areavailable. The higher power ionizes not only the argon working gas, butalso significantly increases the ionization fraction of the sputteredatoms, that is, produces metal ions. The wafer either self-charges to anegative potential or is RF biased to control its DC potential. Themetal ions are accelerated across the plasma sheath as they approach thenegatively biased wafer. As a result, their angular distribution becomesstrongly peaked in the forward direction so that they are drawn deeplyinto the via hole. Overhangs become much less of a problem in IMPsputtering, and bottom coverage and bottom sidewall coverage arerelatively high.

IMP sputtering using a remote plasma source is usually performed at ahigher pressure such as 30 millitorr or higher. The higher pressures anda high-density plasma can produce a very large number of argon ions,which are also accelerated across the plasma sheath to the surface beingsputter deposited. The argon ion energy is often dissipated as heatdirectly into the film being formed. Copper can dewet from tantalumnitride and other barrier materials at elevated temperatures experiencedin IMP, even at temperatures as low at 50 to 75C. Further, the argontends to become embedded in the developing film. IMP can deposit acopper film as illustrated at 136 in the cross-sectional view of FIG. 3,having a surface morphology that is rough or discontinuous. If so, sucha film may not promote hole filling, particularly when the liner isbeing used as the electrode for electroplating.

Another technique for depositing metals is sustained self-sputtering(SSS), as is described by Fu et al. in U.S. patent application Ser. No.08/854,008, filed May 8, 1997 and by Fu in U.S. Pat. No. 6,183,614 B1,Ser. No. 09/373,097, filed Aug. 12, 1999, incorporated by reference intheir entireties. For example, at a sufficiently high plasma densityadjacent a copper target, a sufficiently high density of copper ionsdevelops that the copper ions will resputter the copper target withyield over unity. The supply of argon working gas can then be eliminatedor at least reduced to a very low pressure while the copper plasmapersists. Aluminum is believed to be not readily susceptible to SSS.Some other materials, such as Pd, Pt, Ag, and Au can also undergo SSS.

Depositing copper or other metals by sustained self-sputtering of copperhas a number of advantages. The sputtering rate in SSS tends to be high.There is a high fraction of copper ions which can be accelerated acrossthe plasma sheath and toward a biased wafer, thus increasing thedirectionality of the sputter flux. Chamber pressures may be made verylow, often limited by leakage of backside cooling gas, thereby reducingwafer heating from the argon ions and decreasing scattering of the metalparticles by the argon.

Techniques and reactor structures have been developed to promotesustained self-sputtering. It has been observed that some sputtermaterials not subject to SSS because of sub-unity resputter yieldsnonetheless benefit from these same techniques and structures,presumably because of partial self-sputtering, which results in apartial self-ionized plasma (SIP). Furthermore, it is often advantageousto sputter copper with a low but finite argon pressure even though SSSwithout any argon working gas is achievable. Hence, SIP sputtering isthe preferred terminology for the more generic sputtering processinvolving a reduced or zero pressure of working gas so that SSS is atype of SIP. SIP sputtering has also been described by Fu et al. in U.S.Pat. No. 6,290,825 and by Chiang et al. in U.S. patent Application Ser.No. 09/414,614, filed Oct. 8, 1999, both incorporated herein byreference in their entireties.

SIP sputtering uses a variety of modifications to a fairly conventionalcapacitively coupled magnetron sputter reactor to generate ahigh-density plasma (HDP) adjacent to the target and to extend theplasma and guide the metal ions toward the wafer. Relatively highamounts of DC power are applied to the target, for example, 20 to 40 kWfor a chamber designed for 200 mm wafers. Furthermore, the magnetron hasa relatively small area so that the target power is concentrated in thesmaller area of the magnetron, thus increasing the power densitysupplied to the HDP region adjacent the magnetron. The small-areamagnetron is disposed to a side of a center of the target and is rotatedabout the center to provide more uniform sputtering and deposition.

In one type of SIP sputtering, the magnetron has unbalanced poles,usually a strong outer pole of one magnetic polarity surrounding aweaker inner pole of the other polarity. The magnetic field linesemanating from the stronger pole may be decomposed into not only aconventional horizontal magnetic field adjacent the target face but alsoa vertical magnetic field extending toward the wafer. The vertical fieldlines extend the plasma closer toward the wafer and also guide the metalions toward the wafer. Furthermore, the vertical magnetic lines close tothe chamber walls act to block the diffusion of electrons from theplasma to the grounded shields. The reduced electron loss isparticularly effective at increasing the plasma density and extendingthe plasma across the processing space.

SIP sputtering may be accomplished without the use of RF inductivecoils. The small HDP region is sufficient to ionize a substantialfraction of metal ions, estimated to be between 10 and 25%, whicheffectively sputter coats into deep holes. Particularly at the highionization fraction, the ionized sputtered metal atoms are attractedback to the targets and sputter yet further metal atoms. As a result,the argon working pressure may be reduced without the plasma collapsing.Therefore, argon heating of the wafer is less of a problem, and there isreduced likelihood of the metal ions colliding with argon atoms, whichwould both reduce the ion density and randomize the metal ion sputteringpattern.

A further advantage of the unbalanced magnetron used in SIP sputteringis that the magnetic field from the stronger, outer annular poleprojects far into the plasma processing area towards the wafer. Thisprojecting field has the advantage of supporting a strong plasma over alarger extent of the plasma processing area and to guide ionized sputterparticles towards the wafer. Wei Wang in U.S. patent application Ser.No. 09/612,861 filed Jul. 10, 2000 discloses the use of a coaxialelectromagnetic coil wrapped around the major portion of the plasmaprocess region to create a magnetic field component extending from thetarget to the wafer. The magnetic coil is particularly effective incombining SIP sputtering in a long-throw sputter reactor, that is, onehaving a larger spacing between the target and the wafer because theauxiliary magnetic field supports the plasma and further guides theionized sputter particles. Lai discloses in U.S. Pat. No. 5,593,551 asmaller coil in near the target.

However, SIP sputtering could still be improved. One of its fundamentalproblems is the limited number of variables available in optimizing themagnetic field configuration. The magnetron should be small in order tomaximize the target power density, but the target needs to be uniformlysputtered. The magnetic field should have a strong horizontal componentadjacent the target to maximize the electron trapping there. Somecomponent of the magnetic field should project from the target towardsthe wafer to guide the ionized sputter particles. The coaxial magneticcoil of Wang addresses only some of these problems. The horizontallyarranged permanent magnets disclosed by Lai in U.S. Pat. No. 5,593,551poorly address this effect.

Metal may also be deposited by chemical vapor deposition (CVD) usingmetallo-organic precursors, such as Cu-HFAC-VTMS, commercially availablefrom Schumacher in a proprietary blend with additional additives underthe trade name CupraSelect. A thermal CVD process may be used with thisprecursor, as is very well known in the art, but plasma enhanced CVD(PECVD) is also possible. The CVD process is capable of depositing anearly conformal film even in the high aspect-ratio holes. For example,a film may be deposited by CVD as a thin seed layer, and then PVD orother techniques may be used for final hole filling. However, CVD copperseed layers have often been observed to be rough. The roughness candetract from its use as a seed layer and more particularly as a reflowlayer promoting the low temperature reflow of after deposited copperdeep into hole. Also, the roughness indicates that a relatively thickCVD copper layer of the order of 50 nm may be needed to reliably coat acontinuous seed layer. For the narrower via holes now being considered,a CVD copper seed layer of a certain thickness may nearly fill the hole.However, complete fills performed by CVD can suffer from center seams,which may impact device reliability.

Another, combination technique uses IMP sputtering to deposit a thincopper nucleation layer, sometimes referred to as a flash deposition,and a thicker CVD copper seed layer is deposited on the IMP layer.However, as was illustrated in FIG. 3, the IMP layer 136 can be rough,and the CVD layer tends to conformally follow the roughened substrate.Hence, the CVD layer over an IMP layer will also tend to be rough.

Electrochemical plating (ECP) is yet another copper deposition techniquethat is being developed. In this method, the wafer is immersed in acopper electrolytic bath. The wafer is electrically biased with respectto the bath, and copper electrochemically deposits on the wafer in agenerally conformal process. Electroless plating techniques are alsoavailable. Electroplating and its related processes are advantageousbecause they can be performed with simple equipment at atmosphericpressure, the deposition rates are high, and the liquid processing isconsistent with the subsequent chemical mechanical polishing.

Electroplating, however, imposes its own requirements. A seed andadhesion layer is usually provided on top of the barrier layer, such asof Ta/TaN, to nucleate the electroplated copper and adhere it to thebarrier material. Furthermore, the generally insulating structuresurrounding the via hole 122 requires that an electroplating electrodebe formed between the dielectric layer 114 and the via hole 122.Tantalum and other barrier materials are typically relatively poorelectrical conductors, and the usual nitride sublayer of the barrierlayer 124 which faces the via hole 122 (containing the copperelectrolyte) is even less conductive for the long transverse currentpaths needed in electroplating. Hence, a good conductive seed andadhesion layer are often deposited to facilitate the electroplatingeffectively filling the bottom of the via hole.

A copper seed layer deposited over the barrier layer 124 is typicallyused as the electroplating electrode. However, a continuous, smooth, anduniform film is preferred. Otherwise, the electroplating current will bedirected only to the areas covered with copper or be preferentiallydirected to areas covered with thicker copper. Depositing the copperseed layer presents its own difficulties. An IMP deposited seed layerprovides good bottom coverage in high aspect-ratio holes, but itssidewall coverage can be small such that that the resulting thin filmscan be rough or discontinuous. A thin CVD deposited seed can also be toorough. A thicker CVD seed layer, or CVD copper over IMP copper, mayrequire an excessively thick seed layer to achieve the requiredcontinuity. Also, the electroplating electrode primarily operates on theentire hole sidewalls so that high sidewall coverage is desired. Longthrow provides adequate sidewall coverage, but the bottom coverage maynot be sufficient.

SUMMARIES OF ILLUSTRATIVE EMBODIMENTS

One embodiment of the present invention is directed to sputterdepositing a liner material such as tantalum or tantalum nitride, bycombining long-throw sputtering, self-ionized plasma (SIP) sputtering,inductively-coupled plasma (ICP) resputtering, and coil sputtering inone chamber. Long-throw sputtering is characterized by a relatively highratio of the target-to-substrate distance and the substrate diameter.Long-throw SIP sputtering promotes deep hole coating of both the ionizedand neutral deposition material components. ICP resputtering can reducethe thickness of layer bottom coverage of deep holes to reduce contactresistance. During ICP resputtering, ICP coil sputtering can deposit aprotective layer, particularly on areas such as adjacent the holeopenings where thinning by resputtering may not be desired.

Another embodiment of the present invention is directed to sputterdepositing an interconnect material such as copper, by combininglong-throw sputtering, self-ionized plasma (SIP) sputtering and SIPresputtering in one chamber. Again, long-throw SIP sputtering promotesdeep hole coating of both the ionized and neutral copper components. SIPresputtering can redistribute the deposition to promote good bottomcorner coverage of deep holes.

SIP tends to be promoted by low pressures of less than 5 milliTorr,preferably less than 2 milliTorr, and more preferably less than 1milliTorr. SIP, particularly at these low pressures, tends to bepromoted by magnetrons having relatively small areas to thereby increasethe target power density, and by magnetrons having asymmetric magnetscausing the magnetic field to penetrate farther toward the substrate.Such a process may be used to deposit a seed layer, promoting thenucleation or seeding of an after deposited layer, particularly usefulfor forming narrow and deep vias or contacts through a dielectric layer.A further layer may be deposited by electrochemical plating (ECP). Inanother embodiment, a further layer is be deposited by chemical vapordeposition (CVD).

One embodiment includes an auxiliary magnet array in a magnetron sputterreactor disposed around the chamber close to the wafer and having afirst vertical magnetic polarity. The magnets may either be permanentmagnets or an array of electromagnets having coil axes along the centralaxis of the chamber.

In one embodiment, a rotatable magnetron having a strong outer pole ofthe first magnetic polarity surrounds a weaker pole of the oppositepolarity. The auxiliary magnets are preferably located in the half ofthe processing space near the wafer to pull the unbalanced portion ofthe magnetic field from the outer pole towards the wafer.

Resputtering in an SIP chamber may be promoted in multiple steps inwhich, in one embodiment, biasing of the wafer is increased duringdeposition. Alternatively, power to the target may be decreased duringdeposition to redistribute deposition to the bottom corners of vias andother holes.

There are additional aspects to the present invention as discussedbelow. It should therefore be understood that the preceding is merely abrief summary of some embodiments and aspects of the present invention.Additional embodiments and aspects of the present invention arereferenced below. It should further be understood that numerous changesto the disclosed embodiments can be made without departing from thespirit or scope of the invention. The preceding summary therefore is notmeant to limit the scope of the invention. Rather, the scope of theinvention is to be determined only by the appended claims and theirequivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a via filled with a metallization,which also covers the top of the dielectric, as practiced in the priorart.

FIG. 2 is a cross-sectional view of a via during its filling withmetallization, which overhangs and closes off the via hole.

FIG. 3 is a cross-sectional view of a via having a rough seed layerdeposited by ionized metal plating.

FIG. 4 is a schematic representation of a sputtering chamber usable withan embodiment of the invention.

FIG. 5 is a schematic representation of electrical interconnections ofvarious components of the sputtering chamber of FIG. 4.

FIGS. 6-9B are cross-sectional views of a via liner and metallizationand formation process for a via liner and metallization according to oneembodiment of the invention.

FIG. 10 is a schematic cross-sectional view of a sputter reactorincluding an auxiliary magnet array of the invention.

FIG. 11 is bottom plan view of the top magnetron in the sputter reactorof FIG. 10.

FIG. 12 is an orthographic view of an embodiment of an assemblysupporting an auxiliary magnet array.

FIG. 13 is a schematic cross-sectional view of a sputter reactor inwhich the auxiliary magnet array includes an array of electromagnets.

FIGS. 14A and 14B are cross-sectional views of a via seed layer and viaseed layer formation process according to one embodiment of theinvention.

FIG. 15 is a schematic representation of another sputtering chamberusable with the invention.

FIG. 16 is an exploded view of a portion of FIG. 15 detailing thetarget, shields, isolators and target O-ring.

FIG. 17 is a graph illustrating the relationship between the length ofthe floating shield and the minimum pressure for supporting a plasma.

FIG. 18 is a cross-sectional view of via metallization according toanother embodiment of the invention.

FIGS. 19 and 20 are graphs plotting ion current flux across the waferfor two different magnetrons and different operating conditions.

FIG. 21 is a cross-sectional view of a via metallization according toanother embodiment of the invention.

FIG. 22 is a cross-sectional view of a via metallization according toanother embodiment of the invention.

FIG. 23 is a flow diagram of a plasma ignition sequence which reducesheating of the wafer.

FIG. 24 is a cross-sectional view of via metallization formed inaccordance with a process according to another embodiment of theinvention.

FIG. 25 is a schematic representation of a sputtering chamber inaccordance with another embodiment of the invention.

FIG. 26 is a schematic representation of electrical interconnections ofvarious components of the sputtering chamber of FIG. 25.

FIG. 27 is a schematic view of a integrated processing tool on which theinvention may be practiced.

DESCRIPTIONS OF ILLUSTRATIVE EMBODIMENTS

The distribution between sidewall and bottom coverage in a DC magnetronsputtering reactor can be tailored to produce a metal layer such as aliner layer having a desired profile in a hole or via in a dielectriclayer. A SIP film sputter deposited into a high-aspect ratio via canhave favorable upper sidewall coverage and tends not to developoverhangs. Where desired, bottom coverage may be thinned or eliminatedby ICP resputtering of the bottom of the via. In accordance with oneaspect of the present invention, the advantages of both types ofsputtering can be obtained in a reactor which combines selected aspectsof both SIP and ICP plasma generation techniques, which may be inseparate steps. An example of such a reactor is illustrated generally at150 in FIG. 4. In addition, upper portions of a liner layer sidewall maybe protected from resputtering by sputtering an ICP coil 151 locatedwithin the chamber to deposit coil material onto the substrate.

The reactor 150 may also be used to sputter deposit a metal layer suchas a barrier or liner layer using both SIP and ICP generated plasmas,preferably in combination, but alternatively, alternately. Thedistribution between ionized and neutral atomic flux in a DC magnetronsputtering reactor can be tailored to produce a coating in a hole or viain a dielectric layer. As previously mentioned, a SIP film sputterdeposited into a high-aspect ratio hole can have favorable uppersidewall coverage and tends not to develop overhangs. On the other hand,an ICP generated plasma can increase metal ionization such that a filmsputter deposited into such a hole may have good bottom and bottomcorner coverage. In accordance with yet another aspect of the presentinvention, the advantages of both types of sputtering can be obtained ina reactor, such as the reactor 150, which combines selected aspects ofboth deposition techniques. In addition, coil material may be sputteredto contribute to the deposition layer as well, if desired.

The reactor 150 and various processes for forming liner, barrier andother layers is described in detail in pending U.S. application Ser. No.10/202,778, filed Jul. 25, 2002 (attorney docket No. 4044) and isincorporated by reference in its entirety. As described therein, thereactor 150 of the illustrated embodiment is a DC magnetron type reactorbased on a modification of the Endura PVD Reactor available from AppliedMaterials, Inc. of Santa Clara, Calif. This reactor includes a vacuumchamber 152, usually of metal and electrically grounded, sealed througha target isolator 154 to a PVD target 156 having at least a surfaceportion composed of the material to be sputter deposited on a wafer 158.Although the target sputtering surface is depicted as being planar inthe drawings, ft is appreciated that the target sputtering surface orsurfaces may have a variety of shapes including vaulted and cylindrical.The wafer may be different sizes including 150, 200, 300 and 450 mm. Theillustrated reactor 150 is capable of self-ionized sputtering (SIP) in along-throw mode. This SIP mode may be used in one embodiment in whichcoverage is directed primarily directed to the sidewalls of the hole.The SIP mode may be used to achieve good bottom coverage also.

The reactor 150 also has an RF coil 151 which inductively couples RFenergy into the interior of the reactor. The RF energy provided by thecoil 151 ionizes a precursor gas such as argon to maintain a plasma toresputter a deposition layer using ionized argon to thin bottomcoverage, or to ionize sputtered deposition material to improve bottomcoverage. In one embodiment, rather than maintain the plasma at arelatively high pressure, such as 20-60 mTorr typical for high densityIMP processes, the pressure is preferably maintained at a substantiallylower pressure, such as 1 mTorr for deposition of tantalum nitride or2.5 mTorr for deposition of tantalum, for example. However, a pressurein the range of 0.1 to 40 mTorr may be appropriate, depending upon theapplication. As a consequence, it is believed that the ionization ratewithin the reactor 150 will be substantially lower than that of thetypical high density IMP process. This plasma may be used to resputter adeposited layer or to ionize sputtered deposition material or, or both.Still further, the coil 151 itself may be sputtered to provide aprotective coating on the wafer during resputtering of the materialdeposited onto the wafer for those areas in which thinning of thedeposited material is not desired, or to otherwise provide additionaldeposition material.

In one embodiment, it is believed that good upper sidewall coverage andbottom corner coverage can be achieved in a multi-step process in whichin one step, little or no RF power is applied to the coils. Thus, in onestep, ionization of the sputtered target deposition material would occurprimarily as a result of the self-ionization. Consequently, it isbelieved that good upper sidewall coverage may be achieved. In a secondstep and preferably in the same chamber, RF power may be applied to thecoil 151 while low or no power is applied to the target. In thisembodiment, little or no material would be sputtered from the target 156while ionization of a precursor gas would occur primarily as a result ofthe RF energy inductively coupled by the coil 151. The ICP plasma may bedirected to thin or eliminate bottom coverage by etching or resputteringto reduce barrier layer resistance at the bottom of the hole. Inaddition, the coil 151 may be sputtered to deposit protective materialwhere thinning is not desired. In one embodiment, the pressure may bekept relatively low such that the plasma density is relatively low toreduce ionization of the sputtered deposition material from the coil. Asa result, sputtered coil material can remain largely neutral so as todeposit primarily onto upper sidewalls to protect those portions fromthinning.

Since the illustrated reactor 150 is capable of self-ionized sputtering,deposition material may be ionized not only as a result of the plasmamaintained by the RF coil 151, but also by the sputtering of the target156 itself. When it is desired to deposit a layer with good bottomcoverage, it is believed that the combined SIP and ICP ionizationprocesses provide sufficient ionized material for good bottom and bottomcorner coverage. However, it is also believed that the lower ionizationrate of the low pressure plasma provided by the RF coil 151 allowssufficient neutral sputtered material to remain unionized so as to bedeposited on the upper sidewalls. Thus, it is believed that the combinedsources of ionized deposition material can provide both good uppersidewall coverage as well as good bottom and bottom corner coverage asexplained in greater detail below.

In an alternative embodiment, it is believed that good upper sidewallcoverage, bottom coverage and bottom corner coverage can be achieved ina multi-step process in which in one step, little or no RF power isapplied to the coils. Thus, in one step, ionization of the depositionmaterial would occur primarily as a result of the self-ionization.Consequently, it is believed that good upper sidewall coverage may beachieved. In a second step and preferably in the same chamber, RF powermay be applied to the coil 151. In addition, in one embodiment, thepressure may be raised substantially such that a high density plasma maybe maintained. As a result, it is believed that good bottom and bottomcorner coverage may be achieved in the second step.

A wafer clamp 160 holds the wafer 158 on a pedestal electrode 162.Resistive heaters, refrigerant channels, and thermal transfer gas cavityin the pedestal 162 can be provided to allow the temperature of thepedestal to be controlled to temperatures of less than −40 degrees C. tothereby allow the wafer temperature to be similarly controlled.

To achieve deeper hole coating with a partially neutral flux, thedistance between the target 156 and the wafer 158 can be increased tooperate in the long-throw mode. When used, the target-to-substratespacing is typically greater than half the substrate diameter. In theillustrated embodiment it is preferably greater than 90% wafer diameter(e.g. 190 mm spacings for a 200 mm wafer and 290 mm for a 300 mm wafer),but spacings greater than 80% including greater than 100% and greaterthan 140% of the substrate diameter are believed appropriate also. Formany applications, it is believed that a target to wafer spacing of 50to 1000 mm will be appropriate. Long throw in conventional sputteringreduces the sputtering deposition rate, but ionized sputter particles donot suffer such a large decrease.

A darkspace shield 164 and a chamber shield 166 separated by a seconddielectric shield isolator 168 are held within the chamber 152 toprotect the chamber wall 152 from the sputtered material. In theillustrated embodiment, both the darkspace shield 164 and the chambershield 166 are grounded. However, in some embodiments, shields may befloating or biased to a nonground level. The chamber shield 166 alsoacts as the anode grounding plane in opposition to the cathode target156, thereby capacitively supporting a plasma. If the darkspace shieldis permitted to float electrically, some electrons can deposit on thedarkspace shield 164 so that a negative charge builds up there. It isbelieved that the negative potential could not only repel furtherelectrons from being deposited, but also confine the electrons in themain plasma area, thus reducing the electron loss, sustaininglow-pressure sputtering, and increasing the plasma density, if desired.

The coil 151 is carried on the shield 164 by a plurality of coilstandoffs 180 which electrically insulate the coil 151 from thesupporting shield 164. In addition, the standoffs 180 have labyrinthinepassageways which permit repeated deposition of conductive materialsfrom the target 110 onto the coil standoffs 180 while preventing theformation of a complete conducting path of deposited material from thecoil 151 to the shield 164 which could short the coil 151 to the shield164 (which is typically at ground).

To enable use of the coil as a circuit path, RF power is passed throughthe vacuum chamber walls and through the shield 164 to ends of the coil151. Vacuum feedthroughs (not shown) extend through the vacuum chamberwall to provide RF current from a generator preferably located outsidethe vacuum pressure chamber. RF power is applied through the shield 164to the coil 151 by feedthrough standoffs 182 (FIG. 5), which like thecoil standoffs 180, have labyrinthine passageways to prevent formationof a path of deposited material from the coil 151 to the shield 164which could short the coil 151 to the shield 164.

The plasma darkspace shield 164 is generally cylindrically-shaped. Theplasma chamber shield 166 is generally bowl-shaped and includes agenerally cylindrically shaped, vertically oriented wall 190 to whichthe standoffs 180 and 182 are attached to insulatively support the coil151.

FIG. 5 is a schematic representation of the electrical connections ofthe plasma generating apparatus of the illustrated embodiment. Toattract the ions generated by the plasma, the target 156 is preferablynegatively biased by a variable DC power source 200 at a DC power of1-40 kW, for example. The source 200 negatively biases the target 156 toabout −400 to −600 VDC with respect to the chamber shield 166 to igniteand maintain the plasma. A target power of between 1 and 5 kW istypically used to ignite the plasma while a power of greater than 10 kWis preferred for the SIP sputtering described here. For example, atarget power of 24 kW may be used to deposit tantalum nitride by SIPsputtering and a target power of 20 kW may be used to deposit tantalumby SIP sputtering. During ICP resputtering the target power may bereduced to 100-200 watts, for example to maintain plasma uniformity.Alternatively, the target power may be maintained at a high level iftarget sputtering during ICP resputtering is desired, or may be turnedoff entirely, if desired.

The pedestal 162 and hence the wafer 158 may be left electricallyfloating, but a negative DC self-bias may nonetheless develop on it.Alternatively, the pedestal 162 may be negatively biased by a source 202at −30 v DC to negatively bias the substrate 158 to attract the ionizeddeposition material to the substrate. Other embodiments may apply an RFbias to the pedestal 162 to further control the negative DC bias thatdevelops on it. For example, the bias power supply 202 may be an RFpower supply operating at 13.56 MHz. It may be supplied with RF power ina range of 10 watts to 5 kW, for example, a more preferred range being150 to 300 W for a 200 mm wafer in SIP deposition.

One end of the coil 151 is insulatively coupled through the shield 166by a feedthrough standoff 182 to an RF source such as the output of anamplifier and matching network 204. The input of the matching network204 is coupled to an RF generator 206, which provides RF power atapproximately 1 or 1.5 kW watts for ICP plasma generation for thisembodiment. For example, a power of 1.5 kW for tantalum nitridedeposition and a power of 1 kW for tantalum deposition is preferred. Apreferred range is 50 watts to 10 kW. During SIP deposition, the RFpower to the coil may be turned off if desired. Alternatively, RF powermay be supplied during SIP deposition if desired.

The other end of the coil 151 is also insulatively coupled through theshield 166 by a similar feedthrough standoff 182 to ground, preferablythrough a blocking capacitor 208 which may be a variable capacitor, tosupport a DC bias on the coil 151. The DC bias on the coil 151 and hencethe coil sputtering rate may be controlled through a DC power source 209coupled to the coil 151, as described in U.S. Pat. No. 6,375,810.Suitable DC power ranges for ICP plasma generation and coil sputteringinclude 50 watts to 10 kWatts. A preferred value is 500 watts duringcoil sputtering. DC power to the coil 151 may be turned off during SIPdeposition, if desired.

The above-mentioned power levels may vary of course, depending upon theparticular application. A computer-based controller 224 may beprogrammed to control the power levels, voltages, currents andfrequencies of the various sources in accordance with the particularapplication.

The RF coil 151 may be positioned relatively low in the chamber so thatmaterial sputtered from the coil has a low angle of incidence whenstriking the wafer. As a consequence, coil material may be depositedpreferentially on the upper corners of the holes so as to protect thoseportions of the hole when the hole bottoms are being resputtered by theICP plasma. In the illustrated embodiment, it is preferred that the coilbe positioned closer to the wafer than to the target when the primaryfunction of the coil is to generate a plasma to resputter the wafer andto provide the protective coating during resputtering. For manyapplications, it is believed that a coil to wafer spacing of 0 to 500 mmwill be appropriate. It is appreciated however that the actual positionwill vary, depending upon the particular application. In thoseapplications in which the primary function of the coil is to generate aplasma to ionize deposition material, the coil may be positioned closerto the target. Also, as set forth in greater detail in U.S. Pat. No.6,368,469, entitled Sputtering Coil for Generating a Plasma, filed Jul.10, 1996 (Attorney Docket 1390-CIP/PVD/DV) and assigned to the assigneeof the present application, an RF coil may also be positioned to improvethe uniformity of the deposited layer with sputtered coil material. Inaddition, the coil may have a plurality of turns formed in a helix orspiral or may have as few turns as a single turn to reduce complexityand costs and facilitate cleaning.

A variety of coil support standoffs and feedthrough standoffs may beused to insulatively support the coils. Since sputtering, particularlyat the high power levels associated with SSS, SIP and IP, involves highvoltages, dielectric isolators typically separate the differently biasedparts. As a result, it is desired to protect such isolators from metaldeposition.

The internal structure of the standoffs is preferably labyrinthine asdescribed in greater detail in copending application Ser. No.09/515,880, filed Feb. 29, 2000, entitled “COIL AND COIL SUPPORT FORGENERATING A PLASMA” and assigned to the assignee of the presentapplication. The coil 151 and those portions of the standoffs directlyexposed to the plasma are preferably made of the same material which isbeing deposited. Hence, if the material being deposited is made oftantalum, the outer portions of the standoffs are preferably made oftantalum as well. To facilitate adherence of the deposited material,exposed surfaces of the metal may be treated by bead blasting which willreduce shedding of particles from the deposited material. Besidestantalum, the coil and target may be made from a variety of depositionmaterials including copper, aluminum, and tungsten. The labyrinth shouldbe dimensioned to inhibit formation of a complete conducting path fromthe coil to the shield. Such a conducting path could form as conductivedeposition material is deposited onto the coil and standoffs. It shouldbe recognized that other dimensions, shapes and numbers of passagewaysof the labyrinth are possible, depending upon the particularapplication. Factors affecting the design of the labyrinth include thetype of material being deposited and the number of depositions desiredbefore the standoffs need to be cleaned or replaced. A suitablefeedthrough standoff may be constructed in a similar manner except thatRF power would be applied to a bolt or other conductive member extendingthrough the standoff.

The coil 151 may have overlapping but spaced ends. In this arrangement,the feedthrough standoffs 182 for each end may be stacked in a directionparallel to the plasma chamber central axis between the vacuum chambertarget 156 and the substrate holder 162, as shown in FIG. 4. As aconsequence, the RF path from one end of the coil to the other end ofthe coil can similarly overlap and thus avoid a gap over the wafer. Itis believed that such an overlapping arrangement can improve uniformityof plasma generation, ionization and deposition as described incopending application Ser. No. 09/039,695, filed Mar. 16, 1998 andassigned to the assignee of the present application.

The support standoffs 180 may be distributed around the remainder of thecoil to provide suitable support. In the illustrated embodiments thecoils each have three hub members 504 distributed at 90 degreeseparations on the outer face of each coil. It should be appreciatedthat the number and spacing of the standoffs may be varied dependingupon the particular application.

The coil 151 of the illustrated embodiments is each made of 2 by ¼ inchheavy duty bead blasted tantalum or copper ribbon formed into a singleturn coil. However, other highly conductive materials and shapes may beutilized. For example, the thickness of the coil may be reduced to 1/16inch and the width increased to 2 inches. Also, hollow tubing may beutilized, particularly if water cooling is desired.

The appropriate RF generators and matching circuits are components wellknown to those skilled in the art. For example, an RF generator such asthe ENI Genesis series which has the capability to frequency hunt forthe best frequency match with the matching circuit and antenna issuitable. The frequency of the generator for generating the RF power tothe coil is preferably 2 MHz but it is anticipated that the range canvary at other A.C. frequencies such as, for example, 1 MHz to 200 MHzand non-RF frequencies. These components may be controlled by theprogrammable controller 224 as well.

Returning to FIG. 4, the lower cylindrical portion 296 of the chambershield 166 continues downwardly to well in back of the top of thepedestal 162 supporting the wafer 158. The chamber shield 166 thencontinues radially inwardly in a bowl portion 302 and verticallyupwardly in an innermost cylindrical portion 151 to approximately theelevation of the wafer 158 but spaced radially outside of the pedestal162.

The shields 164, 166 are typically composed of stainless steel, andtheir inner sides may be bead blasted or otherwise roughened to promoteadhesion of the material sputter deposited on them. At some point duringprolonged sputtering, however, the deposited material builds up to athickness that it is more likely to flake off, producing deleteriousparticles. Before this point is reached, the shields should be cleanedor more likely replaced with fresh shields. However, the more expensiveisolators 154, 168 do not need to be replaced in most maintenancecycles. Furthermore, the maintenance cycle is determined by flaking ofthe shields, not by electrical shorting of the isolators.

A gas source 314 supplies a sputtering working gas, typically thechemically inactive noble gas argon, to the chamber 152 through a massflow controller 316. The working gas can be admitted to the top of thechamber or, as illustrated, at its bottom, either with one or more inletpipes penetrating apertures through the bottom of the shield chambershield 166 or through a gap 318 between the chamber shield 166, thewafer clamp 160, and the pedestal 162. A vacuum pump system 320connected to the chamber 152 through a wide pumping port 322 maintainsthe chamber at a low pressure. Although the base pressure can be held toabout 10⁻⁷ Torr or even lower, the pressure of the working gas istypically maintained at between about 1 and 1000 milliTorr inconventional sputtering and to below about 5 millitorr in SIPsputtering. The computer-based controller 224 controls the reactorincluding the DC target power supply 200, the bias power supply 202, andthe mass flow controller 316.

To provide efficient sputtering, a magnetron 330 is positioned in backof the target 156. It has opposed magnets 332, 334 connected andsupported by a magnetic yoke 336. The magnets create a magnetic fieldadjacent the magnetron 330 within the chamber 152. The magnetic fieldtraps electrons and, for charge neutrality, the ion density alsoincreases to form a high-density plasma region 338. The magnetron 330 isusually rotated about the center 340 of the target 156 by a motor-drivenshaft 342 to achieve full coverage in sputtering of the target 156. Toachieve a high-density plasma 338 of sufficient ionization density toallow sustained self-sputtering, the power density delivered to the areaadjacent the magnetron 330 can be made high. This can be achieved, asdescribed by Fu and Chiang in the above cited patents, by increasing thepower level delivered from the DC power supply 200 and by reducing thearea of magnetron 330, for example, in the shape of a triangle or aracetrack. A 60 degree triangular magnetron, which is rotated with itstip approximately coincident with the target center 340, covers onlyabout ⅙ of the target at any time. Coverage of ¼ is the preferredmaximum in a commercial reactor capable of SIP sputtering.

To decrease the electron loss, the inner magnetic pole represented bythe inner magnet 332 and magnetic pole face should have no significantapertures and be surrounded by a continuous outer magnetic polerepresented by the outer magnets 334 and pole face. Furthermore, toguide the ionized sputter particles to the wafer 158, the outer poleshould produce a much higher magnetic flux than the inner pole. Theextending magnetic field lines trap electrons and thus extend the plasmacloser to the wafer 158. The ratio of magnetic fluxes should be at least150% and preferably greater than 200%. Two embodiments of Fu'striangular magnetron have 25 outer magnets and 6 or 10 inner magnets ofthe same strength but opposite polarity. Although depicted incombination with a planar target surface, it is appreciated that avariety of unbalanced magnetrons may be used with a variety of targetshapes to generate self ionized plasmas. The magnets may have shapesother than triangular including circular and other shapes.

When the argon is admitted into the chamber, the DC voltage differencebetween the target 156 and the chamber shield 166 ignites the argon intoa plasma, and the positively charged argon ions are attracted to thenegatively charged target 156. The ions strike the target 156 at asubstantial energy and cause target atoms or atomic clusters to besputtered from the target 156. Some of the target particles strike thewafer 158 and are thereby deposited on it, thereby forming a film of thetarget material. In reactive sputtering of a metallic nitride, nitrogenis additionally admitted into the chamber from a source 343, and itreacts with the sputtered metallic atoms to form a metallic nitride onthe wafer 158.

FIGS. 6-9 b show sequential cross-sectional views of the formation ofliner layers in accordance with a one aspect of the present invention.With reference to FIG. 6, an interlayer dielectric 345 (e.g. silicondioxide) is deposited over a first metal layer (e.g., a first copperlayer 347 a) of an interconnect 348 (FIG. 9 b). A via 349 then is etchedin the interlayer dielectric 345 to expose the first copper layer 347 a.The first metal layer may be deposited using CVD, PVD, electroplating orother such well-known metal deposition techniques, and it is connected,via contacts, through a dielectric layer, to devices formed in theunderlying semiconductor wafer. If the first copper layer 347 a isexposed to oxygen, such as when the wafer is moved from an etchingchamber in which the oxide overlaying the first copper layer is etchedto create apertures for creation of vias between the first copper layerand a second to be deposited metal layer, it can readily form aninsulating/high resistance copper oxide layer 347 a′ thereon.Accordingly, to reduce the resistance of the copper interconnect 348,any copper oxide layer 347 a′ and any processing residue within the via349 may be removed.

A barrier layer 351 may be deposited (e.g., within the sputteringchamber 152 of FIG. 4) over the interlayer dielectric 345 and over theexposed first copper layer 347 a prior to removing the copper oxidelayer 347 a′. The barrier layer 351, preferably comprising tantalum,tantalum nitride, titanium nitride, tungsten or tungsten nitrideprevents subsequently deposited copper layers from incorporating in anddegrading the interlayer dielectric 345 (as previously described).

If, for example, the sputtering chamber 152 is configured for depositionof tantalum nitride layers, a tantalum target 156 is employed.Typically, both argon and nitrogen gas are flowed into the sputteringchamber 152 through the gas inlet 360 (multiple inlets, one for eachgas, may be used), while a power signal is applied to the target 156 viathe DC power supply 200. Optionally, a power signal may also be appliedto the coil 151 via the first RF power supply 206. During steady stateprocessing, nitrogen may react with the tantalum target 156 to form anitride film on the tantalum target 156 so that tantalum nitride issputtered therefrom. Additionally, non-nitrided tantalum atoms are alsosputtered from the target, which atoms can combine with nitrogen to formtantalum nitride in flight or on a wafer (not shown) supported by thepedestal 162.

In operation, a throttle valve operatively coupled to the exhaust outlet362 is placed in a mid-position in order to maintain the depositionchamber 152 at a desired low vacuum level of about 1×10⁻⁸ torr prior tointroduction of the process gas(es) into the chamber. To commenceprocessing within the sputtering chamber 152, a mixture of argon andnitrogen gas is flowed into the sputtering chamber 152 via a gas inlet360. DC power is applied to the tantalum target 156 via the DC powersupply 200 (while the gas mixture continues to flow into the sputteringchamber 152 via the gas inlet 360 and is pumped therefrom via the pump37). The DC power applied to the target 156 causes the argon/nitrogengas mixture to form an SIP plasma and to generate argon and nitrogenions which are attracted to, and strike the target 156 causing targetmaterial (e.g., tantalum and tantalum nitride) to be ejected therefrom.The ejected target material travels to and deposits on the wafer 158supported by the pedestal 162. In accordance with the SIP process, theplasma created by the unbalanced magnetron ionizes a portion of thesputtered tantalum and tantalum nitride. By adjusting the RF powersignal applied to the substrate support pedestal 162, a negative biascan be created between the substrate support pedestal 162 and theplasma. The negative bias between the substrate support pedestal 162 andthe plasma causes tantalum ions, tantalum nitride ions and argon ions toaccelerate toward the pedestal 162 and any wafer supported thereon.Accordingly, both neutral and ionized tantalum nitride may be depositedon the wafer, providing good sidewall and upper sidewall coverage inaccordance with SIP sputtering. In addition, particularly if RF power isoptionally applied to the ICP coil, the wafer may be sputter-etched bythe argon ions at the same time the tantalum nitride material from thetarget 156 deposits on the wafer (i.e., simultaneousdeposition/sputter-etching).

Following deposition of the barrier layer 351, the portion of thebarrier layer 351 at the bottom of the via 349, and the copper oxidelayer 347 a′ (and any processing residue) thereunder, may besputter-etched or resputtered via an argon plasma as shown in FIG. 7, ifthinning or elimination of the bottom is desired. The argon plasma ispreferably generated in this step primarily by applying RF power to theICP coil. Note that during sputter-etching within the sputtering chamber152 (FIG. 4) in this embodiment, the power applied to the target 156 ispreferably either removed or is reduced to a low level (e.g., 100 or 200W) so as to inhibit or prevent significant deposition from the target156. A low target power level, rather than no target power, can providea more uniform plasma and is presently preferred.

ICP argon ions are accelerated toward the barrier layer 351 via anelectric field (e.g., the RF signal applied to the substrate supportpedestal 162 via the second RF power supply 41 of FIG. 4 which causes anegative self bias to form on the pedestal), strike the barrier layer351, and, due to momentum transfer, sputter the barrier layer materialfrom the base of the via aperture and redistribute it along the portionof the barrier layer 351 that coats the sidewalls of the via 349. Theargon ions are attracted to the substrate in a direction substantiallyperpendicular thereto. As a result, little sputtering of the viasidewall, but substantial sputtering of the via base, occurs. Tofacilitate resputtering, the bias applied to the pedestal and the wafermay be 400 watts, for example.

The particular values of the resputtering process parameters may varydepending upon the particular application. Copending or issuedapplication Ser. Nos. 08/768,058; 09/126,890; 09/449,202; 09/846,581;09/490,026; and 09/704,161, describe resputtering processes and areincorporated herein by reference in their entireties.

In accordance with another aspect of the present invention, the ICP coil151 may be formed of liner material such as tantalum in the same manneras the target 156 and sputtered to deposit tantalum nitride onto thewafer while the via bottoms are resputtered. Because of the relativelylow pressure during the resputtering process, the ionization rate of thedeposition material sputtered from the coil 151 is relatively low.Hence, the sputtered material deposited onto the wafer is primarilyneutral material. In addition, the coil 151 is placed relatively low inthe chamber, surrounding and adjacent to the wafer.

Consequently, the trajectory of the material sputtered from the coil 151tends to have a relatively small angle of incidence. Hence, thesputtered material from the coil 151 tends to deposit in a layer 364 onthe upper surface of the wafer and around the openings of the holes orvias in the wafer rather than deep into the wafer holes. This depositedmaterial from the coil 151 may be used to provide a degree of protectionfrom resputtering so that the barrier layer is thinned by resputteringprimarily at the bottom of the holes rather than on the sidewalls andaround the hole openings where thinning of the barrier layer may not bedesired.

Once the barrier layer 351 has been sputter-etched from the via base,the argon ions strike the copper oxide layer 347 a′, and the oxide layeris sputtered to redistribute the copper oxide layer material from thevia base, some or all of the sputtered material being deposited alongthe portion of the barrier layer 351 that coats the sidewalls of the via349. Copper atoms 347 a″, as well, coat the barrier layer 351 and 364disposed on the sidewalls of the via 349. However, because theoriginally deposited barrier layer 351 along with that redistributedfrom the via base to via sidewall is a diffusion barrier to the copperatoms 347 a″, the copper atoms 347 a″ are substantially immobile withinthe barrier layer 351 and are inhibited from reaching the interlayerdielectric 345. The copper atoms 347 a″ which are deposited onto thesidewall, therefore, generally do not generate via-to-via leakagecurrents as they would were they redistributed onto an uncoatedsidewall.

Thereafter, a second liner layer 371 of a second material such astantalum may be deposited (FIG. 8) on the previous barrier layer 351 inthe same chamber 152 or a similar chamber having both an SIP and ICPcapabilities. A tantalum liner layer provides good adhesion between theunderlying tantalum nitride barrier layer and a subsequently depositedmetal interconnect layer of a conductor such as copper. However, in someapplications, it may be preferred to deposit just a barrier layer orjust a liner layer prior to a seed layer or filling the hole.

The second liner layer 371 may be deposited in the same manner as thefirst liner layer 351. That is, the tantalum liner 371 may be depositedin a first SIP step in which the plasma is generated primarily by thetarget magnetron 330. However, nitrogen is not admitted so that tantalumrather than tantalum nitride is deposited. In accordance with SIPsputtering, good sidewall and upper sidewall coverage may be obtained.RF power to the ICP coil 151 may be reduced or eliminated, if desired.

Following deposition of the tantalum liner layer 371, the portion of theliner layer 371 at the bottom of the via 349 (and any processingresidue) thereunder, may be sputter-etched or resputtered via an argonplasma in the same manner as the bottom of the liner layer 351, as shownin FIG. 9 a, if thinning or elimination of the bottom is desired. Theargon plasma is preferably generated in this step primarily by applyingRF power to the ICP coil. Again, note that during sputter-etching withinthe sputtering chamber 152 (FIG. 4), the power applied to the target 156is preferably either removed or is reduced to a low level (e.g., 500 W)so as to inhibit or prevent significant deposition from the target 156during thinning or elimination of the bottom coverage of the secondliner layer 371. In addition, the coil 151 is preferably sputtered todeposit liner material 374 while the argon plasma resputters the layerbottom to protect the liner sidewalls and upper portions from beingthinned substantially during the bottom portion resputtering.

In the above described embodiment, SIP deposition of target material onthe sidewalls of the vias occurs primarily in one step and ICPresputtering of the via bottoms and ICP deposition of coil 151 materialoccurs primarily in a subsequently step. It is appreciated thatdeposition of both target material and coil material on the sidewalls ofthe via 349 can occur simultaneously, if desired. It is furtherappreciated that ICP sputter-etching of the deposited material at thebottom of the via 349 can occur simultaneously with the deposition oftarget and coil material on the sidewalls, if desired. Simultaneousdeposition/sputter-etching may be performed with the chamber 152 of FIG.4 by adjusting the power signals applied to the coil 151, the target 156and the pedestal 162. Because the coil 151 can be used to maintain theplasma, the plasma can sputter a wafer with a low relative bias on thewafer (less than that needed to sustain the plasma). Once the sputteringthreshold has been reached, for a particular wafer bias the ratio of theRF power applied to the wire coil 151 (“RF coil power”) as compared tothe DC power applied to the target 156 (“DC target power”) affects therelationship between sputter-etching and deposition. For instance, thehigher the RF:DC power ratio the more sputter-etching will occur due toincreased ionization and subsequent increased ion bombardment flux tothe wafer. Increasing the wafer bias (e.g., increasing the RF powersupplied to the support pedestal 162) will increase the energy of theincoming ions which will increase the sputtering yield and the etchrate. For example, increasing the voltage level of the RF signal appliedto the pedestal 162 increases the energy of the ions incident on thewafer, while increasing the duty cycle of the RF signal applied to thepedestal 162 increases the number of incident ions.

Therefore, both the voltage level and the duty cycle of the wafer biascan be adjusted to control sputtering rate. In addition, keeping the DCtarget power low will decrease the amount of barrier material availablefor deposition. A DC target power of zero will result in sputter-etchingonly. A low DC target power coupled with a high RF coil power and waferbias can result in simultaneous via sidewall deposition and via bottomsputtering. Accordingly, the process may be tailored for the materialand geometries in question. For a typical 3:1 aspect ratio via on a 200mm wafer, using tantalum or tantalum nitride as the barrier material, aDC target power of 500 W to 1 kW, at an RF coil power of 2 to 3 kW orgreater, with a wafer bias of 250 W to 400 W or greater appliedcontinuously (e.g., 100% duty cycle) can result in barrier deposition onthe wafer sidewalls and removal of material from the via bottom. Thelower the DC target power, the less material will be deposited on thesidewalls. The higher the DC target power, the more RF coil power and/orwafer bias power is needed to sputter the bottom of the via. A 2 kW RFcoil power level on the coil 151 and a 250 W RF wafer power level with100% duty cycle on the pedestal 162, for example may be used forsimultaneous deposition/sputter-etching. It may be desirable toinitially (e.g., for several seconds or more depending on the particulargeometries/materials in question) apply no wafer bias duringsimultaneous deposition/sputter-etching to allow sufficient via sidewallcoverage to prevent contamination of the sidewalls by materialsputter-etched from the via bottom.

For instance, initially applying no wafer bias during simultaneousdeposition/sputter-etching of the via 349 can facilitate formation of aninitial barrier layer on the sidewalls of the interlayer dielectric 345that inhibits sputtered copper atoms from contaminating the interlayerdielectric 345 during the remainder of the deposition/sputter-etchingoperation. Alternatively, deposition/sputter-etching may be performed“sequentially” within the same chamber or by depositing the barrierlayer 351 within a first processing chamber and by sputter-etching thebarrier layer 351 and copper oxide layer 347 a′ within a separate,second processing chamber (e.g., a sputter-etching chamber such asApplied Materials' Preclean II chamber).

Following deposition of the second liner layer 371 and thinning of thebottom coverage, a second metal layer 347 b is deposited (FIG. 9 b) toform the copper interconnect 348. The second copper layer 347 b maydeposited either as a coating or as a copper plug 347 b′ as shown inFIG. 9 b over the second liner layer 371 and over the portion of thefirst copper layer 347 a exposed at the base of each via. The copperlayer 347 b may include a copper seed layer. Because the first andsecond copper layers 347 a, 347 b are in direct contact, rather than incontact through the barrier layer 351 or the second liner layer 371, theresistance of the copper interconnect 348 can be lower as can via-to-vialeakage currents as well. However, it is appreciated that in someapplications, it may be desired to leave a coating of the liner layer orthe barrier layer or both at the bottom of the via.

If the interconnect is formed of a different conductor metal than theliner layer or layers, the interconnect layer may be deposited in asputter chamber having a target of the different conductor metal. Thesputter chamber may be an SIP type or an ICP type. However, at presentdeposition of a copper seed layer is preferred in a chamber of the typedescribed below in connection with FIG. 10. The metal interconnect maybe deposited by other methods in other types of chambers and apparatusincluding CVD and electrochemical plating.

A copper seed layer may be deposited by another plasma sputteringreactor 410 as illustrated in the schematic cross-section view of FIG.10. The reactor 410 and various processes for forming seed and otherlayers is described in copending application Ser. No. 09/993,543, filedNov. 14, 2001 (attorney docket No. 6265) which is incorporated herein byreference in its entirety. As described therein, a vacuum chamber 412includes generally cylindrical sidewalls 414, which are electricallygrounded. Typically, unillustrated grounded replaceable shields arelocated inside the sidewalls 414 to protect them from being sputtercoated, but they act as chamber sidewalls except for holding a vacuum. Asputtering target 416 composed of the metal to be sputtered is sealed tothe chamber 412 through an electrical isolator 418. A pedestal electrode422 supports a wafer 424 to be sputter coated in parallel opposition tothe target 416. A processing space is defined between the target 416 andthe wafer 424 inside of the shields.

A sputtering working gas, preferably argon, is metered into the chamberfrom a gas supply 426 through a mass flow controller 428. Anunillustrated vacuum pumping system maintains the interior of thechamber 412 at a very low base pressure of typically 10⁻⁸ Torr or less.During plasma ignition, the argon pressure is supplied in an amountproducing a chamber pressure of approximately 5 millitorr, but as willbe explained later the pressure is thereafter decreased. A DC powersupply 434 negatively biases the target 416 to approximately −600 VDCcausing the argon working gas to be excited into a plasma containingelectrons and positive argon ions. The positive argon ions are attractedto the negatively biased target 416 and sputter metal atoms from thetarget.

The invention is particularly useful with SIP sputtering in which asmall nested magnetron 436 is supported on an unillustrated back platebehind the target 416. The chamber 412 and target 416 are generallycircularly symmetric about a central axis 438. The SIP magnetron 436includes an inner magnet pole 440 of a first vertical magnetic polarityand a surrounding outer magnet pole 442 of the opposed second verticalmagnetic polarity. Both poles are supported by and magnetically coupledthrough a magnetic yoke 444. The yoke 444 is fixed to a rotation arm 446supported on a rotation shaft 448 extending along the central axis 4438.A motor 450 connected to the shaft 448 causes the magnetron 436 torotate about the central axis 438.

In an unbalanced magnetron, the outer pole 442 has a total magnetic fluxintegrated over its area that is larger than that produced by the innerpole 440, preferably having a ratio of the magnetic intensities of atleast 150%. The opposed magnetic poles 440, 442 create a magnetic fieldinside the chamber 412 that is generally semi-toroidal with strongcomponents parallel and close to the face of the target 416 to create ahigh-density plasma there to thereby increase the sputtering rate andincrease the ionization fraction of the sputtered metal atoms. Becausethe outer pole 442 is magnetically stronger than the inner pole 440, afraction of the magnetic field from the outer pole 442 projects fartowards the pedestal 422 before it loops back to behind the outer pole442 to complete the magnetic circuit.

An RF power supply 454, for example, having a frequency of 13.56 MHz isconnected to the pedestal electrode 422 to create a negative self-biason the wafer 424. The bias attracts the positively charged metal atomsacross the sheath of the adjacent plasma, thereby coating the sides andbottoms of high aspect-ratio holes in the wafer, such as, inter-levelvias.

In SIP sputtering, the magnetron is small and has a high magneticstrength and a high amount of DC power is applied to the target so thatthe plasma density rises to above 10¹⁰ cm⁻³ near the target 416. In thepresence of this plasma density, a large number of sputtered atoms areionized into positively charged metal ions. The metal ion density ishigh enough that a large number of them are attracted back to the targetto sputter yet further metal ions. As a result, the metal ions can atleast partially replace the argon ions as the effective working speciesin the sputtering process. That is, the argon pressure can be reduced.The reduced pressure has the advantage of reducing scattering anddeionization of the metal ions. For copper sputtering, under someconditions it is possible in the process called sustainedself-sputtering (SSS) to completely eliminate the argon working gas oncethe plasma has been ignited. For aluminum or tungsten sputtering, SSS isnot possible, but the argon pressure can be substantially reduced fromthe pressures used in conventional sputtering, for example, to less than1 milliTorr.

In one embodiment of the invention, an auxiliary array 460 of permanentmagnets 462 is positioned around the chamber sidewalls 414 and isgenerally positioned in the half of the processing space towards thewafer 424. In this embodiment, the auxiliary magnets 462 have the samefirst vertical magnetic polarity as the outer pole 442 of the nestedmagnetron 436 so as to draw down the unbalanced portion of the magneticfield from the outer pole 442. In the embodiment described in detailbelow, there are eight permanent magnets, but any number of four or moredistributed around the central axis 438 would provide similarly goodresults. It is possible to place the auxiliary magnets 462 inside thechamber sidewalls 414 but preferably outside the thin sidewall shield toincrease their effective strength in the processing region. However,placement outside the sidewalls 414 is preferred for overall processingresults.

The auxiliary magnet array is generally symmetrically disposed about thecentral axis 438 to produce a circularly symmetric magnetic field. Onthe other hand, the nested magnetron 436 has a magnetic fielddistribution is asymmetrically disposed about the central axis 438although, when it is averaged over the rotation time, it becomessymmetric. There are many forms of the nested magnetron 436. Thesimplest though less preferred form has a button center pole 440surround by an circularly annular outer pole 442 such that its field issymmetric about an axis displaced from the chamber axis 438 and thenested magnetron axis is rotated about the chamber axis 438. Thepreferred nested magnetron has a triangular shape, illustrated in thebottom plan view of FIG. 11, with an apex near the central axis 438 anda base near the periphery of the target 416. This shape is particularlyadvantageous because the time average of the magnetic field is moreuniform than for a circular nested magnetron.

The effective magnetic field at a particular instant of time during therotation cycle is shown by the dotted lines of FIG. 10. A semi-toroidalfield BM provides a strong horizontal component close to and parallel tothe face of the target 416, thereby increasing the density of theplasma, the rate of sputtering, and the ionization fraction of sputteredparticles. An auxiliary field BA1, BA2 is the sum of the field from theauxiliary magnet array 460 and from the unbalanced portion of the fieldof the nested magnetron 436. On the side of the chamber away from thenested magnetron 436, the component BA1 from the unbalanced portion ofthe field of the nested magnetron 436 predominates, and it does notextend far towards the wafer 424. However, near the chamber sidewall 414on the side of the nested magnetron 436, the auxiliary magnet 462 isstrongly coupled to the outer magnet pole 442, resulting in a magneticfield component BA2 that projects far towards the wafer 424. Out of theplane of the illustration, the magnetic field component is ancombination of the two components BA1, BA2.

This structure effects the result that a strong vertical magnetic fieldis produced near to and along a substantial length of the chambersidewall 414 in a region beneath the nested magnetron 436 sweeping aboutit because of the alignment of the magnetic polarities of the auxiliarymagnets 442 and the strong outer magnetic poles 442. As a result, thereis a strong vertical magnetic field on the exterior side of the chamber412 adjacent the area of the target 416 being most strongly sputtered.This projecting field is effective for both extending the region of theplasma and for guiding the ionized particles to the wafer 424.

The auxiliary magnet array 460 may be implemented by the use of twosemi-circular magnet carriers 470, one of which is illustratedorthographically in FIG. 12. Each carrier 470 includes four recesses 472facing its interior and sized to receive a respective magnet assembly474 including one magnet 462. The magnet assembly 474 includes anarc-shaped upper clamp member 476 and a lower clamp member 478, whichcapture the cylindrically shaped magnet 462 into recesses when twoscrews 480 tighten the two clamp members 476, 478 together. The carriers470 and clamp members 476, 478 may be formed of non-magnetic materialsuch as aluminum. The lower clamp member 478 has a length to fit intothe recess 472 but the upper clamp member 476 has end portions extendingbeyond the recess 472 and through which are drilled two through holes482. Two screws 484 pass through respective through holes to allow thescrews 484 to be fixed in tapped holes 486 in the magnet carrier 470,thereby fixing the magnet 462 in position on the magnet carrier 470. Twoso assembled semi-circular magnet carrier 470 are placed in a ringaround the chamber wall 414 and fixed to it by conventional fasteningmeans. This structure places the magnets 462 directly adjacent theexterior of the chamber wall 414.

The solenoidal magnetic field created inside the electromagnetic coil ofWei Wang is substantially more uniform across the diameter of thereactor chamber than is the peripheral dipole magnetic field created byan annular array of permanent magnets. However, it is possible to createa similarly shaped dipole field by replacing the permanent magnets 462with, as illustrated in the cross-sectional view of FIG. 13, an annulararray of electromagnetic coils 490 arranged around the periphery of thechamber wall. The coils 490 are typically wrapped as helices aboutrespective axes parallel to the central axis 438 and are electricallypowered to produce nearly identical magnetic dipole fields inside thechamber. Such a design has the advantage of allowing the quickadjustment of the auxiliary magnetic field strength and even thepolarity of the field.

This invention has been applied to SIP sputtering of copper. While aconventional SIP reactor sputters a copper film having a non-uniformityof 9% determined by sheet resistance measurements, it is believed thatthe auxiliary magnetron can be optimized to produce a non-uniformity ofonly 1% in some embodiments. The improvement in uniformity may beaccompanied by a reduced deposition rate in some applications, for thedeposition of thin copper seed layers in deep holes, which may bedesirable for improved process control in some applications.

Although the invention has been described for use in an SIP sputterreactor, the auxiliary permanent magnet array can be advantageouslyapplied to other target and power configurations such as the annularlyvaulted target of the SIP⁺ reactor of U.S. Pat. No. 6,251,242, thehollow cathode target of U.S. Pat. No. 6,179,973 or “IonizedPhysical—vapor deposition Using a Hollow-cathode Magnetron Source forAdvanced Metallization” by Klawuhn et al, J. Vac. Sci Technology,July/August 2000, the inductively coupled IMP reactor of U.S. Pat. No.6,045,547 or a self ion sputtering (SIS) system which controls ion fluxto a substrate using an ion reflector as described, for example, in “CuDual Damascene Process for 0.13 micrometer Technology Generation usingSelf Ion Sputtering (SIS) with Ion Reflector” by Wada et al., IEEE,2000. Other magnetron configurations may be used, such as balancedmagnetrons and stationary ones. Further, the polarity of the auxiliarymagnets may be parallel or anti-parallel to the magnetic polarity of theouter pole of the top magnetron. Other materials may be sputteredincluding Al, Ta, Ti, Co, W etc. and the nitrides of several of thesewhich are refractory metals.

The auxiliary magnet array thus provides additional control of themagnetic field useful in magnetron sputtering. However, to achievedeeper hole coating with a partially neutral flux, it is desirable toincrease the distance between the target 416 and the wafer 424, that is,to operate in the long-throw mode. As discussed above in connection withthe chamber of FIG. 4, in long-throw, the target-to-substrate spacing istypically greater than half the substrate diameter. When used in SIPcopper seed deposition, it is preferably greater than 140% waferdiameter (e.g. 290 mm spacing) for a 200 mm wafer and greater than 130%(e.g. 400 mm spacing) for a 300 mm wafer, but spacings greater than 80%including greater than 90% and greater than 100% of the substratediameter are believed appropriate also. For many applications, it isbelieved that a target to wafer spacing of 50 to 1000 mm will beappropriate. Long throw in conventional sputtering reduces thesputtering deposition rate, but ionized sputter particles do not suffersuch a large decrease.

One embodiment of a structure which can be produced by the chamber ofFIG. 4 and the chamber of FIG. 10 is a via illustrated in cross-sectionin FIG. 14 a. A seed copper layer 492 is deposited by the chamber ofFIG. 10 in the via hole 494 over the liner layers formed in the chamberof FIG. 4, which may include one or more barrier and liner layers suchas the aforementioned TaN barrier 351, 364 and Ta liner layers 371, 374under conditions promoting SIP and ICP. The SIP copper layer 492 may bedeposited, for example, to a blanket thickness of 50 to 300 nm or morepreferably of 80 to 200 nm. The SIP copper seed layer 492 preferably hasa thickness in the range of 2 to 20 nm on the via sidewalls, morepreferably 7 to 15 nm. In view of the narrow holes, the a sidewallthickness in excess of 50 nm may not be optimal for some applications.The quality of the film can in some applications be improved bydecreasing the pedestal temperature to less than 0 degrees C. andpreferably to less than −40 degrees C. In such applications quick SIPdeposition is advantageous.

If, for example, the sputtering chamber 410 is configured for depositionof copper layers, a copper target 416 is employed. In operation, athrottle valve operatively coupled to the chamber exhaust outlet isplaced in a mid-position in order to maintain the deposition chamber 410at a desired low vacuum level of about 1×10⁻⁸ torr prior to introductionof the process gas(es) into the chamber. To commence processing withinthe sputtering chamber 410, argon gas is flowed into the sputteringchamber 410 via a gas inlet 428. For deposition of copper seed in a longthrow SIP chamber, a very low pressure is preferred, such as 0-2 mTorr.In the illustrated embodiment, a pressure of 0.2 mTorr is suitable. DCpower is applied to the copper target 416 via the DC power supply 434(while the gas mixture continues to flow into the sputtering chamber 410via the gas inlet 360 and is pumped therefrom via a suitable pump). Thepower applied to the target 416 may range for a copper target in a rangeof 20-60 kWatts for a 200 mm wafer. In one example, the power supply 434can apply 38 kWatts to the copper target 416 at a voltage of −600 VDC.For larger wafers such as 300 mm wafers, it is anticipated that largervalues such as 56 kWatts may be appropriate. Other values may also beused, depending upon the particular application.

The DC power applied to the target 416 causes the argon to form an SIPplasma and to generate argon ions which are attracted to, and strike thetarget 416 causing target material (e.g., copper) to be ejectedtherefrom. The ejected target material travels to and deposits on thewafer 424 supported by the pedestal 422. In accordance with the SIPprocess, the plasma created by the unbalanced magnetron ionizes aportion of the sputtered copper. By adjusting the RF power signalapplied to the substrate support pedestal 422, a negative bias can becreated between the substrate support pedestal 422 and the plasma.

The power applied to the pedestal 422 may range for copper seeddeposition in a range of 0-1200 watts. In one example, the RF powersupply 454 can apply 300 watts to the pedestal 422 for a 200 mm wafer.For larger wafers such as 300 mm wafers, it is anticipated that largervalues may be appropriate. Other values may also be used, depending uponthe particular application.

The negative bias between the substrate support pedestal 422 and theplasma causes copper ions and argon ions to accelerate toward thepedestal 422 and any wafer supported thereon. Accordingly, both neutraland ionized copper may be deposited on the wafer, providing good bottom,sidewall and upper sidewall coverage in accordance with SIP sputtering.In addition, the wafer may be sputter-etched by the argon ions at thesame time the copper material from the target 416 deposits on the wafer(i.e., simultaneous deposition/sputter-etching).

Following or during deposition of the seed layer 492, the portion of theseed layer 492 at the bottom 496 of the via 494 may be sputter-etched orresputtered via an argon plasma as shown in FIG. 14B, if redistributionof the bottom is desired. The bottom 496 may be redistributed toincrease coverage thickness of the bottom corner areas 498 of the copperseed layer as shown in FIG. 14B. In many applications, it is preferredthat the copper seed layer bottom 496 not be completely removed toprovide adequate seed layer coverage throughout the via.

The argon plasma is preferably generated in this resputtering step asSIP plasma by applying power to the target and to the pedestal. SIPargon ions are accelerated toward the seed layer 492 via an electricfield (e.g., the RF signal applied to the substrate support pedestal 422via the second RF power supply 454 of FIG. 10 which causes a negativeself bias to form on the pedestal), strike the seed layer 492, and, dueto momentum transfer, sputter the seed layer material from the base ofthe via aperture and redistribute it along the portion 498 of the seedlayer 492 that coats the bottom corners of the via 349.

The argon ions are attracted to the substrate in a directionsubstantially perpendicular thereto. As a result, little sputtering ofthe via sidewall, but substantial sputtering of the via base, occurs.Note that during resputtering of the copper seed layer within thesputtering chamber 410 (FIG. 10) in this embodiment, the power appliedto the pedestal 422 may be increased to a higher value, such as 600-1200watts, or 900 watts, for example, to facilitate redistribution of thecopper seed layer bottom. Thus, in this example, the pedestal power israised from a level below 600 watts (e.g. 300 watts) to a level greaterthan 600 watts (e.g. 900 watts) to enhance the redistribution effect ofthe resputtering.

In another example, the power applied to the target 416 may be reducedto a lower value, such as below 30 kWatts or 28 kWatts, for example, soas to inhibit deposition from the target 416 to facilitateredistribution of the copper seed layer bottom. A low target powerlevel, rather than no target power, can provide a more uniform plasmaand is presently preferred in those embodiments in which target power isreduced for seed layer bottom redistribution. Thus, in this example, thetarget power is lowered from a level above 30000 (e.g. 38 kWatts) to alevel lower than 30000 watts, (e.g. 28 kWatts) to enhance resputtering.

In yet another example, the resputtering of the copper seed layer bottommay be performed simultaneously throughout the copper seed layerdeposition such that the target and pedestal power levels may bemaintained relatively constant (such as 38 kWatts and 300 watts,respectively) during the seed layer deposition. In other embodiments,target power reductions may be alternated or combined with pedestalpower increases to facilitate seed layer bottom redistribution.

The particular values of the resputtering process parameters may varydepending upon the particular application. Copending or issuedapplication Ser. Nos. 08/768,058; 09/126,890; 09/449,202; 09/846,581;09/490,026; and 09/704,161, describe resputtering processes and areincorporated herein by reference in their entireties.

The SIP copper seed layer 492 has good bottom and sidewall coverage andenhanced bottom corner coverage. After the copper seed layer 492 isdeposited, the hole is filled with a copper layer 18, as in FIG. 1,preferably by electro-chemical plating using the seed layer 492 as oneof the electroplating electrodes. Alternatively, the smooth structure ofthe SIP copper seed layer 492 also promotes reflow or higher-temperaturedeposition of copper by standard sputtering or physical vapor deposition(PVD).

The chambers of FIGS. 4 and 10 utilize both ionized and neutral atomicflux. As described in U.S. Pat. No. 6,398,929 (attorney docket No. 3920)which is incorporated herein by reference in its entirety, thedistribution between ionized and neutral atomic flux in a DC magnetronsputtering reactor can be tailored to produce an advantageous layer in ahole in a dielectric layer. Such a layer can be used either by itself orin combination with a copper seed layer deposited by chemical vapordeposition (CVD) over a sputtered copper nucleation layer. A copperliner layer is particularly useful as a thin seed layer forelectroplated copper.

The DC magnetron sputtering reactors of the prior art have been directedto either conventional, working gas sputtering or to sustainedself-sputtering. The two approaches emphasize different types ofsputtering. It is, on the other hand, preferred that the reactor for thecopper liner combine various aspects of the prior art to control thedistribution between ionized copper atoms and neutrals. An example ofsuch a reactor 550 is illustrated in the schematic cross-sectional viewof FIG. 15. The reactors of FIGS. 4, 10 and 13 may utilize these aspectsof the reactor of FIG. 15 which is also based on a modification of theEndura PVD Reactor available from Applied Materials, Inc. of SantaClara, Calif. The reactor 550 includes a vacuum chamber 552, usually ofmetal and electrically grounded, sealed through a target isolator 554 toa PVD target 556 having at least a surface portion composed of thematerial, in this case copper or a copper alloy, to be sputter depositedon a wafer 558. The alloying element is typically present to less than 5wt %, and essentially pure copper may be used if adequate barriers areotherwise formed. A wafer clamp 560 holds the wafer 558 on a pedestalelectrode 562. Unillustrated resistive heaters, refrigerant channels,and thermal transfer gas cavity in the pedestal 562 allow thetemperature of the pedestal to be controlled to temperatures of lessthan −40 degrees C. to thereby allow the wafer temperature to besimilarly controlled.

A floating shield 564 and a grounded shield 566 separated by a seconddielectric shield isolator 568 are held within the chamber 552 toprotect the chamber wall 552 from the sputtered material. The groundedshield 566 also acts as the anode grounding plane in opposition to thecathode target 556, thereby capacitively supporting a plasma. Someelectrons deposit on the floating shield 564 so that a negative chargebuilds up there. The negative potential not only repels furtherelectrons from being deposited, but also confines the electrons in themain plasma area, thus reducing the electron loss, sustaininglow-pressure sputtering, and increasing the plasma density.

Details of the target and shields are illustrated in the explodedcross-sectional view of FIG. 16. The target 556 includes an aluminum ortitanium backing plate 570 to which is soldered or diffusion bonded acopper target portion 572. A flange 573 of the backing plate 570 restson and is vacuum sealed through a polymeric target O-ring 574 to thetarget isolator 554, which is preferably composed of a ceramic such asalumina. The target isolator 554 rests on and is vacuum sealed throughan adaptor O-ring 575 to the chamber 552, which in fact may be analuminum adaptor sealed to the main chamber body. A metal clamp ring 576has on its inner radial side an upwardly extending annular rim 577.Unillustrated bolts fix the metal clamp ring 576 to an inwardlyextending ledge 578 of the chamber 552 and capture a flange 579 of thegrounded shield 566. Thereby, the grounded shield 566 is mechanicallyand electrically connected to the grounded chamber 552.

The shield isolator 568 freely rests on the clamp ring 576 and may bemachined from a ceramic material such as alumina. It is compact but hasa relatively large height of approximately 165 mm compared to a smallerwidth to provide strength during the temperature cycling of the reactor.The lower portion of the shield isolator 568 has an inner annular recessfitting outside of the rim 577 of the clamp ring 576. The rim 577 notonly acts to center inner diameter of the shield isolator 568 withrespect to the clamp ring 576 but also acts as a barrier against anyparticles generated at the sliding surface 580 between the ceramicshield isolator 568 and the metal ring clamp 576 from reaching the mainprocessing area.

A flange 581 of the floating shield 564 freely rests on the shieldisolator 568 and has a tab or rim 582 on its outside extendingdownwardly into an annular recess formed at the upper outer corner ofthe shield isolator 568. Thereby, the tab 582 centers the floatingshield 564 with respect to the target 556 at the outer diameter of theshield isolator 568. The shield tab 582 is separated from the shieldisolator 568 by a narrow gap which is sufficiently small to align theplasma dark spaces but sufficiently large to prevent jamming of theshield isolator 568, and the floating shield 581 rests on the shieldisolator 568 in a sliding contact area 583 inside and above the tab 582.

A narrow channel 584 is formed between a head 585 of the floating shield564 and the target 556. It has a width of about 2 mm to act as a plasmadark space. The narrow channel 584 continues in a path extending evenmore radially inward than illustrated past a downwardly projecting ridge586 of the backing plate flange 574 to an upper back gap 584 a betweenthe shield head 585 and the target isolator 554. The structure of theseelements and their properties are similar to those disclosed by Tang etal. in U.S. patent application Ser. No. 09/191,253, filed Oct. 30, 1998.The upper back gap 584 a has a width of about 1.5 mm at roomtemperature. When the shield elements are temperature cycled, they tendto deform. The upper back gap 584 a, having a smaller width than thenarrow channel 584 next to the target 556, is sufficient to maintain aplasma dark space in the narrow channel 584. The back gap 584 acontinues downwardly into a lower back gap 584 b between the shieldisolator 568 and the ring clamp 576 on the inside and the chamber body552 on the outside. The lower back gap 584 b serves as a cavity tocollect ceramic particles generated at the sliding surfaces 580, 583between the ceramic shield isolator 568 and the clamp ring 576 and thefloating shield 564. The shield isolator 568 additionally includes ashallow recess 583 a on its upper inner corner to collect ceramicparticles from the sliding surface 583 on its radially inward side.

The floating shield 564 includes a downwardly extending, wide uppercylindrical portion 588 extending downwardly from the flange 581 andconnected on its lower end to a narrower lower cylindrical portion 590through a transition portion 592. Similarly, the grounded shield 566 hasan wider upper cylindrical portion 594 outside of and thus wider thanthe upper cylindrical portion 588 of the floating shield 564. Thegrounded upper cylindrical portion 594 is connected on its upper end tothe grounded shield flange 580 and on its lower end to a narrowed lowercylindrical portion 596 through a transition portion 598 thatapproximately extends radially of the chamber. The grounded lowercylindrical portion 596 fits outside of and is thus wider than thefloating lower cylindrical portion 590; but it is smaller than thefloating upper cylindrical portion 564 by a radial separation of about 3mm. The two transition portions 592, 598 are both vertically andhorizontally offset. A labyrinthine narrow channel 600 is thereby formedbetween the floating and grounded shields 564, 566 with the offsetbetween the grounded lower cylindrical portion 596 and floating uppercylindrical portion 564 assuring no direct line of sight between the twovertical channel portions. A purpose of the channel 600 is toelectrically isolate the two shields 564, 566 while protecting the clampring 576 and the shield isolator 568 from copper deposition.

The lower portion of the channel 600 between the lower cylindricalportions 590, 596 of the shields 564, 566 has an aspect ratio of 4:1 orgreater, preferably 8:1 or greater. The lower portion of the channel 600has an exemplary width of 0.25 cm and length of 2.5 cm, with preferredranges being 0.25 to 0.3 cm and 2 to 3 cm. Thereby, any copper ions andscattered copper atoms penetrating the channel 600 are likely to have tobounce several times from the shields and at least stopped by the uppergrounded cylindrical portion 594 before they can find their way furthertoward the clamp ring 576 and the shield isolator 568. Any one bounce islikely to result in the ion being absorbed by the shield. The twoadjacent 90 degrees turns or bends in the channel 600 between the twotransition portions 592, 598 further isolate the shield isolator 568from the copper plasma. A similar but reduced effect could be achievedwith 60 degrees bends or even 45 degrees bends but the more effective 90degrees bends are easier to form in the shield material. The 90 degreesturns are much more effective because they increase the probability thatcopper particles coming from any direction will have at least one highangle hit and thereby lose most their energy to be stopped by the uppergrounded cylindrical portion 594. The 90 degrees turns also shadow theclamp ring 576 and shield isolator 568 from being directly irradiated bycopper particles. It has been found that copper preferentially depositson the horizontal surface at the bottom of the floating transitionportion 592 and on the vertical upper grounded cylindrical portion 594,both at the end of one of the 90 degrees turns. Also, the convolutechannel 600 collects ceramic particles generated from the shieldisolator 568 during processing on the horizontal transition portion 598of the grounded shield 566. It is likely that such collected particlesare pasted by copper also collected there.

Returning to the large view of FIG. 15, the lower cylindrical portion596 of the grounded shield 566 continues downwardly to well in back ofthe top of the pedestal 562 supporting the wafer 558. The groundedshield 566 then continues radially inwardly in a bowl portion 602 andvertically upwardly in an innermost cylindrical portion 604 toapproximately the elevation of the wafer 558 but spaced radially outsideof the pedestal 562.

The shields 564, 566 are typically composed of stainless steel, andtheir inner sides may be bead blasted or otherwise roughened to promoteadhesion of the copper sputter deposited on them. At some point duringprolonged sputtering, however, the copper builds up to a thickness thatit is likely to flake off, producing deleterious particles. Before thispoint is reached, the shields should be cleaned or more likely replacedwith fresh shields. However, the more expensive isolators 554, 568 donot need to be replaced in most maintenance cycles. Furthermore, themaintenance cycle is determined by flaking of the shields, not byelectrical shorting of the isolators.

As mentioned, the floating shield 564 accumulates some electron chargeand builds up a negative potential. Thereby, it repels further electronloss to the floating shield 564 and thus confines the plasma nearer thetarget 556. Ding et al. have disclosed a similar effect with a somewhatsimilar structure in U.S. Pat. No. 5,736,021. However, the floatingshield 564 of FIG. 16 has its lower cylindrical portion 590 extendingmuch further away from the target 556 than does the corresponding partof Ding et al., thereby confining the plasma over a larger volume.However, the floating shield 564 electrically shields the groundedshield 566 from the target 556 so that is should not extend too far awayfrom the target 556. If it is too long, it becomes difficult to strikethe plasma; but, if it is too short, electron loss is increased so thatthe plasma cannot be sustained at lower pressure and the plasma densityfalls. An optimum length has been found at which the bottom tip 606 ofthe floating shield 566, as shown in FIG. 16, is separated 6 cm from theface of the target 556 with a total axial length of the floating shield566 being 7.6 cm. Three different floating shields have been tested forthe minimum pressure at which copper sputtering is maintained. Theresults are shown in FIG. 17 for 1 kW and 18 kW of target power. Theabscissa is expressed in terms of total shield length, the separationbetween shield tip 606 and target 556 being 1.6 cm less. A preferredrange for the separation is 5 to 7 cm, and that for the length is 6.6 to8.6 cm. Extending the shield length to 10 cm reduces the minimumpressure somewhat but increases the difficulty of striking the plasma.

Referring again to FIG. 15, a selectable DC power supply 610 negativelybiases the target 556 to about −400 to −600 VDC with respect to thegrounded shield 566 to ignite and maintain the plasma. A target power ofbetween 1 and 5 kW is typically used to ignite the plasma while a powerof greater than 10 kW is preferred for the SIP sputtering describedhere. Conventionally, the pedestal 562 and hence the wafer 558 are leftelectrically floating, but a negative DC self-bias nonetheless developson it. On the other hand, some designs use a controllable power supply612 to apply a DC or RF bias to the pedestal 562 to further control thenegative DC bias that develops on it. In the tested configuration, thebias power supply 612 is an RF power supply operating at 13.56 MHz. Itmay be supplied with up to 600 W of RF power, a preferred range being350 to 550 W for a 200 mm wafer.

A gas source 614 supplies a sputtering working gas, typically thechemically inactive noble gas argon, to the chamber 552 through a massflow controller 616. The working gas can be admitted to the top of thechamber or, as illustrated, at its bottom, either with one or more inletpipes penetrating apertures through the bottom of the shield groundedshield 566 or through a gap 618 between the grounded shield 566, thewafer clamp 560, and the pedestal 562. A vacuum pump system 620connected to the chamber 552 through a wide pumping port 622 maintainsthe chamber at a low pressure. Although the base pressure can be held toabout 10⁻⁷ Torr or even lower, the pressure of the working gas istypically maintained at between about 1 and 1000 milliTorr inconventional sputtering and to below about 5 milliTorr in SIPsputtering. A computer-based controller 624 controls the reactorincluding the DC target power supply 610, the bias power supply 612, andthe mass flow controller 616.

To provide efficient sputtering, a magnetron 630 is positioned in backof the target 556. It has opposed magnets 632, 634 connected andsupported by a magnetic yoke 636. The magnets create a magnetic fieldadjacent the magnetron 630 within the chamber 552. The magnetic fieldtraps electrons and, for charge neutrality, the ion density alsoincreases to form a high-density plasma region 638. The magnetron 630 isusually rotated about the center 640 of the target 556 by a motor-drivenshaft 642 to achieve full coverage in sputtering of the target 556. Toachieve a high-density plasma 638 of sufficient ionization density toallow sustained self-sputtering of copper, the power density deliveredto the area adjacent the magnetron 630 must be made high. This can beachieved, as described by Fu in the above cited patents, by increasingthe power level delivered from the DC power supply 610 and by reducingthe area of magnetron 630, for example, in the shape of a triangle or aracetrack. A 601 triangular magnetron, which is rotated with its tipapproximately coincident with the target center 640, covers only about ⅙of the target at any time. Coverage of ¼ is the preferred maximum in acommercial reactor capable of SIP sputtering.

To decrease the electron loss, the inner magnetic pole represented bythe inner magnet 632 and unillustrated magnetic pole face should have nosignificant apertures and be surrounded by a continuous outer magneticpole represented by the outer magnets 634 and unillustrated pole face.Furthermore, to guide the ionized sputter particles to the wafer 558,the outer pole should produce a much higher magnetic flux than the innerpole. The extending magnetic field lines trap electrons and thus extendthe plasma closer to the wafer 558. The ratio of magnetic fluxes shouldbe at least 150% and preferably greater than 200%. Two embodiments ofFu's triangular magnetron have 25 outer magnets and 6 or 10 innermagnets of the same strength but opposite polarity.

When the argon is admitted into the chamber, the DC voltage differencebetween the target 556 and the grounded shield 566 ignites the argoninto a plasma, and the positively charged argon ions are attracted tothe negatively charged target 556. The ions strike the target 556 at asubstantial energy and cause target atoms or atomic clusters to besputtered from the target 556. Some of the target particles strike thewafer 558 and are thereby deposited on it, thereby forming a film of thetarget material. In reactive sputtering of a metallic nitride, nitrogenis additionally admitted into the chamber, and it reacts with thesputtered metallic atoms to form a metallic nitride on the wafer 558.

The illustrated chamber is capable of self-ionized sputtering of copperincluding sustained self-sputtering. In this case, after the plasma hasbeen ignited, the supply of argon may be cut off in the case of SSS, andthe copper ions have sufficiently high density to resputter the coppertarget with a yield of greater than unity. Alternatively, some argon maycontinue to be supplied, but at a reduced flow rate and chamber pressureand perhaps with insufficient target power density to support puresustained self-sputtering but nonetheless with a significant but reducedfraction of self-sputtering. If the argon pressure is increased tosignificantly above 5 milliTorr, the argon will remove energy from thecopper ions, thus decreasing the self-sputtering. The wafer biasattracts the ionized fraction of the copper particle deep into the hole.

However, to achieve deeper hole coating with a partially neutral flux,it is desirable to increase the distance between the target 556 and thewafer 558, that is, to operate in the long-throw mode. In long-throw,the target-to-substrate spacing is typically greater than half thesubstrate diameter. When used, it is preferably greater than 90% waferdiameter, but spacings greater than 80% including 100% and 140% of thesubstrate diameter are believed appropriate also. The throws mentionedin the examples of the embodiment are referenced to 200 mm wafers. Longthrow in conventional sputtering reduces the sputtering deposition rate,but ionized sputter particles do not suffer such a large decrease.

The controlled division between conventional (argon-based) sputteringand sustained self-sputtering (SSS) allows the control of thedistribution between neutral and ionized sputter particles. Such controlis particularly advantageous for the sputter deposition of a copper seedlayer in a high aspect-ratio via hole. The control of the ionizationfraction of sputtered atoms is referred to as self-ionized plasma (SIP)sputtering.

One embodiment of a structure produced by the invention is a viaillustrated in cross-section in FIG. 18. A seed copper layer 650 isdeposited in the via hole 22 over the barrier layer 24 using, forexample, the long-throw sputter reactor of FIG. 15 and under conditionspromoting SIP. The SIP copper layer 650 may be deposited, for example,to a blanket thickness of 50 to 300 nm or more preferably of 80 to 200nm. The SIP copper seed layer 650 preferably has a thickness in therange of 2 to 20 nm on the via sidewalls, more preferably 7 to 15 nm. Inview of the narrow holes, the sidewall thickness should not exceed 50nm. The quality of the film is improved by decreasing the pedestaltemperature to less than 0 degrees C. and preferably to less than −40degrees C. so that the coolness afforded by the quick SIP depositionbecomes important.

The SIP copper seed layer 650 has good bottom coverage and enhancedsidewall coverage. It has been experimentally observed to be muchsmoother than either IMP or CVD copper deposited directly over thebarrier layer 24. After the copper seed layer 650 is deposited, the holeis filled with a copper layer 118, as in FIG. 1, preferably byelectrochemical plating using the seed layer 650 as one of theelectroplating electrodes. However, the smooth structure of the SIPcopper seed layer 650 also promotes reflow or higher-temperaturedeposition of copper by standard sputtering or physical vapor deposition(PVD).

Several experiments were performed in SIP depositing such a seed layerinto a 0.20 μm-wide via hole in 1.2 μm of oxide. With atarget-to-substrate spacing of 290 mm, a chamber pressure of less than0.1 millitorr (indicating SSS mode) and 14 kW of DC power applied to thetarget with a 601 triangular magnetron, a deposition producing 0.2 μm ofblanket thickness of the copper on top of the oxide produces 18 nm onthe via bottom and about 12 nm on the via sidewalls. Deposition times of30s and less are typical. When the target power is increased to 18 kW,the bottom coverage increases to 37 nm without a significant change insidewall thickness. The higher bottom coverage at higher power indicatesa higher ionization fraction. For both cases, the deposited copper filmis observed to be much smoother than seen for IMP or CVD copper.

The SIP deposition is relatively fast, between 0.5 to 1.0 μm/min incomparison to an IMP deposition rate of no more than 0.2 μm/min. Thefast deposition rate results in a short deposition period and, incombination with the absence of argon ion heating, significantly reducesthe thermal budget. It is believed that the low-temperature SIPdeposition results in a very smooth copper seed layer.

A 290 mm throw was used with the standard triangular magnetron of Fuutilizing ten inner magnets and twenty-five outer ones. The ion currentflux was measured as a function of radius from the target center undervarious conditions. The results are plotted in the graph of FIG. 19.Curve 660 is measured for 16 kW of target power and 0 millitorr ofchamber pressure. Curves 662, 664, 664 are measured for 18 kW of targetpower and chamber pressures of 0, 0.2, and 1 milliTorr respectively.These currents correspond to an ion density of between 10¹¹ and 10¹²cm⁻³, as compared to less than 10⁹ cm⁻³ with a conventional magnetronand sputter reactor. The zero-pressure conditions were also used tomeasure the copper ionization fraction. The spatial dependences areapproximately the same with the ionization fraction varying betweenabout 10% and 20% with a direct dependence on the DC target power. Therelatively low ionization fraction demonstrate that SIP without longthrow would has a large fraction of neutral copper flux which would havethe unfavorable deep filling characteristics of conventional PVD.Results indicate that operation at higher power is preferred for betterstep coverage due to the increased ionization.

The tests were then repeated with the number of inner magnets in the Fumagnetron being reduced to six. That is, the second magnetron hadimproved uniformity in the magnetic flux, which promotes a uniformsputtered ion flux toward the wafer. The results are plotted in FIG. 20.Curve 668 displays the ion current flux for 12 kW of target power and 0milliTorr pressure; curve 670, for 18 kW. Curves for 14 kW and 16 kW areintermediate. Thus, the modified magnetron produces a more uniform ioncurrent across the wafer, which is again dependent on the target powerwith higher power being preferred.

The relatively low ionization fractions of 10% to 20% indicate asubstantial flux of neutral copper compared to the 90% to 100% fractionof IMP. While wafer bias can guide the copper ions deep into the holes,long throw accomplishes much the same for the copper neutrals.

A series of tests were used to determine the combined effects of throwand chamber pressure upon the distribution of sputter particles. At zerochamber pressure, a throw of 140 mm produces a distribution of about 45degrees; a throw of 190 mm, about 35 degrees; and, a throw of 290 mm,about 25 degrees. The pressure was varied for a throw of 190 mm. Thecentral distribution remains about the same for 0, 0.5 and 1 milliTorr.However, the low-level tails are pushed out almost 101 for the highestpressure, indicative of the scattering of some particles. These resultsindicate that acceptable results are obtained below 5 milliTorr, but apreferred range is less than 2 milliTorr, a more preferred range is lessthan 1 millitorr, and a most preferred range is 0.2 milliTorr and less.Also, as expected, the distribution is best for the long throws.

A SIP film deposited into a high-aspect ratio hole has favorable uppersidewall coverage and tends not to develop overhangs. On the other hand,an IMP film deposited into such a hole has better bottom and bottomcorner coverage, but the sidewall film tends to have poor coverage andbe rough. The advantages of both types of sputtering can be combined byusing a two-step copper seed sputter deposition. In a first step, copperis deposited in an IMP reactor producing a high-density plasma, forexample, by the use of RF inductive source power. Exemplary depositionconditions are 20 to 60 milliTorr of pressure, 1 to 3 kW of RF coilpower, 1 to 2 kW of DC target power, and 150 W of bias power. The firststep provides good though rough bottom and bottom sidewall coverage. Ina second and preferably subsequent step, copper is deposited in an SIPreactor of the sort described above producing a lesser degree of copperionization. Exemplary deposition conditions are 1 Torr pressure, 18 to24 kW of DC target power and 500 W of bias power. The second stepprovides good smooth upper sidewall coverage and further smoothes outthe already deposited IMP layer. The blanket deposition thicknesses forthe two steps preferably range from 50 to 100 nm for the IMP depositionand 100 to 200 nm for the SIP layer. Blanket thicknesses may be a ratioof 30:70 to 70:30. Alternatively, the SIP layer can be deposited beforethe IMP layer. After the copper seed layer is sputter deposited by thetwo-step process, the remainder of the hole is filled, for example, byelectroplating.

The SIP sidewall coverage may become a problem for very narrow,high-aspect ratio vias. Technology for 0.13 μm vias and smaller is beingdeveloped. Below about 100 nm of blanket thickness, the sidewallcoverage may become discontinuous. As shown in the cross-sectional viewof FIG. 21, the unfavorable geometry may cause a SIP copper film 680 tobe formed as a discontinuous films including voids or otherimperfections 682 on the via sidewall 30. The imperfection 682 may be anabsence of copper or such a thin layer of copper that it cannot actlocally as an electroplating cathode. Nonetheless, the SIP copper film680 is smooth apart from the imperfections 682 and well nucleated. Inthese challenging geometries, it is then advantageous to deposit acopper CVD seed layer 684 over the SIP copper nucleation film 680. Sinceit is deposited by chemical vapor deposition, it is generally conformaland is well nucleated by the SIP copper film 680. The CVD seed layer 684patches the imperfections 682 and presents a continuous, non-rough seedlayer for the later copper electroplating to complete the filling of thehole 22. The CVD layer may be deposited in a CVD chamber designed forcopper deposition, such as the CuxZ chamber available from AppliedMaterials using the previously described thermal process.

Experiments were performed in which 20 nm of CVD copper was deposited onalternatively a SIP copper nucleation layer and an IMP nucleation layer.The combination with SIP produced a relatively smooth CVD seed layerwhile the combination with IMP produced a much rougher surface in theCVD layer to the point of discontinuity.

The CVD layer 684 may be deposited to a thickness, for example, in therange of 5 to 20 nm. The remainder of the hole may then be filled withcopper by other methods. The very smooth seed layer produced by CVDcopper on top of the nucleation layer of SIP copper provides forefficient hole filling of copper by electroplating or conventional PVDtechniques in the narrow vias being developed. In particular forelectroplating, the smooth copper nucleation and seed layer provides acontinuous and nearly uniform electrode for powering the electroplatingprocess.

In the filling of a via or other hole having a very high-aspect ratio,it may be advantageous to dispense with the electroplating and instead,as illustrated in the cross-sectional view of FIG. 22, deposit asufficiently thick CVD copper layer 688 over the SIP copper nucleationlayer 680 to completely fill the via. An advantage of CVD filling isthat it eliminates the need for a separate electroplating step. Also,electroplating requires fluid flows which may be difficult to control athole widths below 0.13 μm.

An advantage of the copper bilayer of this embodiment of the inventionis that it allows the copper deposition to be performed with arelatively low thermal budget. Tantalum tends to dewet from oxide athigher thermal budgets. IMP has many of the same coverage advantages fordeep hole filling, but IMP tends to operate at a much higher temperaturebecause it produces a high flux of energetic argon ions which dissipatetheir energy in the layer being deposited. Further, IMP invariablyimplants some argon into the deposited film. On the contrary, therelatively thin SIP layer is deposited at a relatively high rate and theSIP process is not inherently hot because of the absence of argon. Also,the SIP deposition rates are much faster than with IMP so that any hotdeposition is that much shorter, by up to a factor of a half.

The thermal budget is also reduced by a cool ignition of the SIP plasma.A cool plasma ignition and processing sequence is illustrated in theflow diagram of FIG. 23. After the wafer has been inserted through theload lock valve into the sputter reactor, the load lock valve is closed,and in step 690 gas pressures are equilibrated. The argon chamberpressure is raised to that used for ignition, typically between 2 andabout 5 to 10 milliTorr, and the argon backside cooling gas is suppliedto the back of the wafer at a backside pressure of about 5 to 10 Torr.In step 692, the argon is ignited with a low level of target power,typically in the range of 1 to 5 kW. After the plasma has been detectedto ignite, in step 694, the chamber pressure is quickly ramped down, forexample over 3s, with the target power held at the low level. Ifsustained self-sputtering is planned, the chamber argon supply is turnedoff, but the plasma continues in the SSS mode. For self-ionized plasmasputtering, the argon supply is reduced. The backside cooling gascontinues to be supplied. Once the argon pressure has been reduced, instep 696, the target power is quickly ramped up to the intendedsputtering level, for example, 10 to 24 kW or greater for a 200 mmwafer, chosen for the SIP or SSS sputtering. It is possible to combinethe steps 694, 696 by concurrently reducing pressure and ramping up thepower. In step 698, the target continues to be powered at the chosenlevel for a length of time necessary to sputter deposit the chosenthickness of material. This ignition sequence is cooler than using theintended sputtering power level for ignition. The higher argon pressurefacilitates ignition but would deleteriously affect the sputteredneutrals if continued at the higher power levels desired for sputterdeposition. At the lower ignition power, very little copper is depositeddue to the low deposition rate at the reduced power. Also, the pedestalcooling keep the wafer chilled through the ignition process.

Many of the features of the apparatus and process of the invention canbe applied to sputtering not involving long throw.

Although the invention is particularly useful at the present time forcopper inter-level metallization and barrier and liner deposition, thedifferent aspects of the invention may be applied to sputtering othermaterials and for other purposes.

As described in copending application Ser. No. 10/202,778, filed Jul.25, 2002 (attorney docket No. 4044), which is incorporated herein byreference in its entirety, the interconnect layer or layers may also bedeposited in a sputter chamber similar to the chamber 152 (FIG. 4) whichgenerates both SIP and ICP plasmas. If deposited in a chamber such asthe chamber 152, the target 156 would be formed of the depositionmaterial, such as copper, for example. In addition, the ICP coil 151 maybe formed of the same deposition material as well, particularly if coilsputtering is desired for some or all of the interconnect metaldeposition.

As previously mentioned, the illustrated chamber 152 is capable ofself-ionized sputtering of copper including sustained self-sputtering.In this case, after the plasma has been ignited, the supply of argon maybe cut off in the case of SSS, and the copper ions have sufficientlyhigh density to resputter the copper target with a yield of greater thanunity. Alternatively, some argon may continue to be supplied, but at areduced flow rate and chamber pressure and perhaps with insufficienttarget power density to support pure sustained self-sputtering butnonetheless with a significant but reduced fraction of self-sputtering.If the argon pressure is increased to significantly above 5 milliTorr,the argon will remove energy from the copper ions, thus decreasing theself-sputtering. The wafer bias attracts the ionized fraction of thecopper particle deep into the hole.

However, to achieve deeper hole coating with a partially neutral flux,it is desirable to increase the distance between the target 156 and thewafer 158, that is, to operate in the long-throw mode as discussedabove. The controlled division among self-ionized plasma (SIP)sputtering, inductively coupled plasma (ICP) sputtering and sustainedself-sputtering (SSS) allows the control of the distribution betweenneutral and ionized sputter particles. Such control is particularlyadvantageous for the sputter deposition of a copper seed layer in a highaspect-ratio via hole. The control of the ionization fraction ofsputtered is achieved by mixing self-ionized plasma (SIP) sputtering andinductively coupled plasma (ICP) sputtering.

One embodiment of a structure in accordance with the present inventionis a via illustrated in cross-section in FIG. 24. A copper seed layer700 is deposited in a via hole 702 over the liner layer 704 (which mayinclude one or more barrier and liner layers such as the aforementionedTaN barrier and Ta liner layers) using, for example, a long-throwsputter reactor of the type shown in FIG. 4 and under conditionspromoting combined SIP and ICP and/or alternating SIP and ICP. Here, thereactor would have a target which includes the copper or other seedlayer deposition material. The SIP-ICP copper layer 700 may bedeposited, for example, to a blanket thickness of 50 to 300 nm or morepreferably of 80 to 200 nm. The SIP-ICP copper seed layer 700 preferablyhas a thickness in the range of 2 to 20 nm on the via sidewalls, morepreferably 7 to 15 nm. In view of the narrow holes, the sidewallthickness should not exceed 50 nm. The quality of the film is improvedby decreasing the pedestal temperature to less than 0 degrees C. andpreferably to less than 40 degrees C. so that the coolness afforded bythe quick SIP deposition becomes important.

It is believed that the SIP-ICP copper seed layer 700 will have goodbottom coverage and enhanced sidewall coverage. As explained in greaterdetail below, the copper seed layer 700 may be resputtered either in aseparate step or during the initial deposition to redistribute thecopper deposition material to increase coverage at the inside bottomcorners of the via while usually leaving a thinner coverage in thecentral portion of the via bottom. After the copper seed layer 700 isdeposited (and redistributed, if desired), the hole may be filled with acopper layer similar to the copper layer 347 b′ of FIG. 14 b, preferablyby electrochemical plating using the seed layer 700 as one of theelectroplating electrodes. However, the smooth structure of the SIP-ICPcopper seed layer 700 also promotes reflow or higher-temperaturedeposition of copper by standard sputtering or physical vapor deposition(PVD).

In one embodiment, an SIP-ICP layer may be formed in a process whichcombines selected aspects of both SIP and ICP deposition techniques inone step, referred to herein generally as an SIP-ICP step. In addition,a reactor 715 in accordance with an alternative embodiment has a secondcoil 716 in addition to the coil 151 as shown in FIG. 25. In the samemanner as the coil 151, one end of the coil 716 is insulatively coupledthrough a darkspace shield 164′ by a feedthrough standoff 182 to theoutput of an amplifier and matching network 717 (FIG. 26). The input ofthe matching network 717 is coupled to an RF generator 718. The otherend of the coil 716 is insulatively coupled through the shield 164′ by afeedthrough standoff 182 to ground, via a blocking capacitor 719, toprovide a DC bias on the coil 716. The DC bias may be controlled by aseparate DC source 721.

In an ICP or combined SIP-ICP step, RF energy is applied to one or bothof the RF coils 151 and 716 at 1-3 kW and a frequency of 2 Mhz, forexample. The coils 151 and 716 when powered, inductively couple RFenergy into the interior of the reactor. The RF energy provided by thecoils ionizes a precursor gas such as argon to maintain a plasma toionize sputtered deposition material. However, rather than maintain theplasma at a relatively high pressure, such as 20-60 mTorr typical forhigh density IMP processes, the pressure is preferably maintained at asubstantially lower pressure, such as 2 mTorr, for example. As aconsequence, it is believed that the ionization rate within the reactor150 will be substantially lower than that of the typical high densityIMP process.

Furthermore as discussed above, the illustrated reactor 150 is alsocapable of self-ionized sputtering in a long-throw mode. As aconsequence, deposition material may be ionized not only as a result ofthe low pressure plasma maintained by the RF coil or coils, but also bythe plasma self-generated by the DC magnetron sputtering of the target.It is believed that the combined SIP and ICP ionization processes canprovide sufficient ionized material for good bottom and bottom cornercoverage. However, it is also believed that the lower ionization rate ofthe low pressure plasma provided by the RF coils 151 and 716 allowssufficient neutral sputtered material to remain unionized so as to bedeposited on the upper sidewalls by the long-throw capability of thereactor. Thus, it is believed that the combined SIP and ICP sources ofionized deposition material can provide both good upper sidewallcoverage as well as good bottom and bottom corner coverage. In anotherembodiment, the power to the coils 151 and 716 may be alternated suchthat in one step, the power to the upper coil 726 is eliminated orreduced relative to the power applied to the lower coil 151. In thisstep, the center of the inductively coupled plasma is shifted away fromthe target and closer to the substrate. Such an arrangement may reduceinteraction between the self ionized plasma generated adjacent thetarget, and the inductively coupled plasma maintained by one or more ofthe coils. As a consequence, a higher proportion of neutral sputteredmaterial might be maintained.

In a second step, the power may be reversed such that the power to thelower coil 151 is eliminated or reduced relative to the power applied tothe upper coil 716. In this step, the center of the inductively coupledplasma may be shifted toward the target and away from the substrate.Such an arrangement may increase the proportion of ionized sputteredmaterial.

In another embodiment, the layer may be formed in two or more steps inwhich in one step, referred to herein generally as an SIP step, littleor no RF power is applied to either coil. In addition, the pressurewould be maintained at a relatively low level, preferably below 5 mTorr,and more preferably below 2 mTorr such as at 1 mTorr, for example.Furthermore, the power applied to the target would be relatively highsuch as in the range of 18-24 kW DC, for example. A bias may also beapplied to the substrate support at a power level of 500 watts forexample. Under these conditions, it is believed that ionization of thedeposition material would occur primarily as a result of (SIP)self-ionization plasma. Combined with the long-throw mode arrangement ofthe reactor, it is believed that good upper sidewall coverage may beachieved with low overhang. The portion of the layer deposited in thisinitial step may be in the range of 1000-2000 angstroms, for example.

In a second step, referred to generally herein as an ICP step, andpreferably in the same chamber, RF power may be applied to one or bothof the coils 151 and 716. In addition, in one embodiment, the pressuremay be raised substantially such that a high density plasma may bemaintained. For example, the pressure may be raised to 20-60 mTorr, theRF power to the coil raised to a range of 1-3 kW, the DC power to thetarget reduced to 1-2 kW and the bias to the substrate support reducedto 150 watts. Under these conditions, it is believed the ionization ofthe deposition material would occur primarily as a result ofhigh-density ICP. As a result, good bottom and bottom corner coveragemay be achieved in the second step. Power may be applied to both coilssimultaneously or alternating, as described above.

After the copper seed layer is sputter deposited by a process combiningSIP and ICP, the remainder of the hole may be filled by the same oranother process. For example, the remainder of the hole may be filled byelectroplating or CVD.

It should be appreciated that the order of the SIP and ICP steps may bereversed and that some RF power may be applied to one or more coils inthe SIP step and that some self-ionization may be induced in the ICPstep. In addition, sustained self sputtering (SSS) may be induced in oneor more steps. Hence, process parameters including pressure, power andtarget-wafer distance may be varied, depending upon the particularapplication, to achieve the desired results.

As previously mentioned in the coils 151 and 516 may be operatedindependently or together. In one embodiment, the coils may be operatedtogether in which the RF signal applied to one coil is phase shiftedwith respect to the other RF signal applied to the other coil so as togenerate a helicon wave. For example, the RF signals may be phaseshifted by a fraction of a wavelength as described in U.S. Pat. No.6,264,812.

One embodiment of present invention includes an integrated processpreferably practiced on an integrated multi-chamber tool, such as theEndura 5500 platform schematically illustrated in plan view in FIG. 27.The platform is functionally described by Tepman et al. in U.S. Pat. No.5,186,718.

Wafers which have been already etched with via holes or other structurein a dielectric layer are loaded into and out of the system through twoindependently operated load lock chambers 732, 734 configured totransfer wafers into and out of the system from wafer cassettes loadedinto the respective load lock chambers. After a wafer cassette has beenloaded into a load lock chamber 732, 734, the chamber is pumped to amoderately low pressure, for example, in the range of 10⁻³ to 10⁻⁴ Torr,and a slit valve between that load lock chamber and a first wafertransfer chamber 736 is opened. The pressure of the first wafer transferchamber 736 is thereafter maintained at that low pressure.

A first robot 738 located in the first transfer chamber 736 transfer thewafer from the cassette to one of two degassing/orienting chambers 740,742, and then to a first plasma pre-clean chamber 744, in which ahydrogen or argon plasma cleans the surface of the wafer. If a CVDbarrier layer is being deposited, the first robot 738 then passes thewafer to a CVD barrier chamber 746. After the CVD barrier layer isdeposited, the robot 738 passes the wafer into a pass through chamber748, from whence a second robot 750 transfers it to a second transferchamber 752. Slit valves separate the chambers 744, 746, 748 from thefirst transfer chamber 736 so as to isolate processing and pressurelevels.

The second robot 750 selectively transfers wafers to and from reactionchambers arranged around the periphery. A first IMP sputter chamber 754may be dedicated to the deposition of copper. An SIP sputter chamber 756similar to the chamber 410 described above is dedicated to thedeposition of an SIP copper seed or nucleation layer. This chambercombines SIP for bottom and sidewall coverage and resputtering forimproved bottom corner coverage in either a one step or a multi-stepprocess as discussed above. Also, at least part of the barrier layer,of, for example, Ta/TaN is being deposited by SIP sputtering and coilsputtering and ICP resputtering, and therefore an SIP-ICP sputterchamber 760 is dedicated to a sputtering a refractory metal, possibly ina reactive nitrogen plasma. The same SIP-ICP chamber 760 may be used fordepositing the refractory metal and its nitride. A CVD chamber 758 isdedicated to the deposition of a copper nucleation, seed or liner layeror to complete the filling of the hole or both. Each of the chambers754, 756, 758, 760 is selectively opened to the second transfer chambers752 by slit valves. It is possible to use a different configuration. Forexample, an IMP chamber 754 may be replaced by a second CVD copperchamber, particularly if CVD is used to complete the hole filling.

After the low-pressure processing, the second robot 750 transfers thewafer to an intermediately placed thermal chamber 762, which may be acool down chamber if the preceding processing was hot or may be a rapidthermal processing (RTP) chamber is annealing of the metallization isrequired. After thermal treatment, the first robot 738 withdraws thewafer and transfers it back to a cassette in one of the load lockchambers 732, 734. Of course, other configurations are possible withwhich the invention can be practiced depending on the steps of theintegrated process.

The entire system is controlled by a computer-based controller 770operating over a control bus 772 to be in communication withsub-controllers associated with each of the chambers. Process recipesare read into the controller 770 by recordable media 774, such asmagnetic floppy disks or COD-ROMs, insertable into the controller 770,or over a communication link 776.

Many of the features of the apparatus and process of the invention canbe applied to sputtering not involving long throw. Although theinvention is particularly useful at the present time for tantalum andtantalum nitride liner layer deposition and copper inter-levelmetallization, the different aspects of the invention may be applied tosputtering other materials and for other purposes. Provisionalapplication No. 60/316,137 filed Aug. 30, 2001 is directed to sputteringand resputtering techniques and is incorporated herein by reference.

It will, of course, be understood that modifications of the presentinvention, in its various aspects, will be apparent to those skilled inthe art, some being apparent only after study, others being matters ofroutine mechanical and process design. Other embodiments are alsopossible, their specific designs depending upon the particularapplication. As such, the scope of the invention should not be limitedby the particular embodiments herein described but should be definedonly by the appended claims and equivalents thereof.

1. A method of depositing metal into a hole having an aspect ratio of atleast 4:1 and formed in a dielectric layer of a substrate, comprising:sputter depositing a deposition material comprising a metal in said holein a self-ionized plasma in a chamber; and after said sputter depositingin a self-ionized plasma, sputter depositing a deposition materialcomprising a metal in said hole in an inductively coupled plasma in saidchamber.
 2. The method of claim 1 further comprising filling said holewith a metal.
 3. The method of claim 2 wherein said filling compriseselectroplating.
 4. The method of claim 1 wherein said sputter depositingin an inductively coupled plasma further includes resputtering in saidinductively coupled plasma deposition material deposited in saidself-ionized plasma.
 5. The method of claim 4 wherein said resputteringincludes removing deposition material deposited on a bottom of saidhole.
 6. The method of claim 1 wherein said sputter depositing in aself-ionized plasma deposits a deposition material comprising at leastone of tantalum and tantalum nitride.
 7. The method of claim 1 whereinsaid sputter depositing in a self-ionized plasma deposits a depositionmaterial comprising copper.
 8. The method of claim 1 wherein saidsputter depositing in an inductively coupled plasma deposits adeposition material comprising at least one of tantalum and tantalumnitride.
 9. The method of claim 1 wherein said sputter depositing in aninductively coupled plasma deposits a deposition material comprisingcopper.
 10. The method of claim 1, wherein said sputter depositing in aninductively coupled plasma at least partially uses RF inductive couplingwith a coil internal to the chamber containing said inductively coupledplasma to form said inductively coupled plasma.
 11. A tool fordepositing metal into a hole having an aspect ratio of at least 4:1 andformed in a dielectric layer of a substrate, comprising: a transferchamber; an IMP sputter chamber coupled to said transfer chamber andadapted to form an inductively coupled plasma in said IMP chamber andadapted to sputter deposit a deposition material comprising a metal insaid hole in said inductively coupled plasma wherein said IMP chamberhas a pedestal adapted to support and bias said substrate; an SIPchamber coupled to said transfer chamber and adapted to form aself-ionized plasma in said SIP chamber and adapted to sputter deposit adeposition material comprising a metal in said hole in said self-ionizedplasma, wherein said SIP chamber has sidewalls arranged around a centralaxis; a pedestal for supporting said substrate in said SIP chamber; asputtering target positioned in opposition to said pedestal along saidcentral axis, a processing space being defined in a region between saidpedestal, said target, and said sidewalls; a magnetron positioned on aside of said target opposite said processing space; and auxiliarymagnets disposed at least partially around said processing space havinga first magnetic polarity along said central axis and wherein saidtarget is spaced from said pedestal by a throw distance that is greaterthan 50% of a diameter of the substrate; and a controller adapted tocontrol said pedestal of said IMP chamber to bias said substrate toattract ions of said inductively coupled plasma to resputter depositionmaterial.
 12. The tool of claim 11 wherein said resputtering includesremoving deposition material deposited on a bottom of said hole.
 13. Thetool of claim 11 wherein said SIP chamber has a sputter targetcomprising tantalum.
 14. The tool of claim 11 wherein said SIP chamberhas a sputter target comprising copper.
 15. The tool of claim 11 whereinsaid IMP chamber has a sputter target comprising tantalum.
 16. The toolof claim 11 wherein said IMP chamber has a sputter target comprisingcopper.
 17. The tool of claim 11, wherein said IMP chamber has aninternal RF coil adapted to inductively couple RF energy to saidinductively coupled plasma.